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#1 2020-12-30 19:59:40

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 21,860

Coast to Coast starship flights

I am sure that the intent of a flight from Launch pad to Landing pad to compete with the likes of the Concorde and others was part of the dream for its use.
Preparing for “Earth to Earth” space travel and a competition with supersonic airliners

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Commercial spaceflight companies are preparing to enter a new market: suborbital flights from one place to another on Earth. Aiming for fast transportation for passengers and cargo, these systems are being developed by a combination of established companies, such as SpaceX and Virgin Galactic, and new ones like Astra.

Technical and business challenges lie ahead for this new frontier, and an important piece is the coming wave of supersonic aircraft which could offer safer but slower alternatives to spaceflight. These two different approaches could face off in the 2020s to be the future of transportation on Earth.

Suborbital space travel

The most prevalent concept for suborbital Earth to Earth transportation comes from none other than Elon Musk and SpaceX. Primarily designed for transporting large payloads to Mars for the purpose of colonization, the next generation Starship launch system offers a bonus capability for transporting large amounts of cargo around Earth.

Musk first presented this idea in 2017, envisioning suborbital spaceflights between spaceports offshore from major cities. These launch and landing facilities would be far enough to reduce the disruption of rocket launch noise levels and sonic booms produced by landing vehicles, connected to land by a high speed form of transportation such as speedboats or a hyperloop.

Originally, these Earth to Earth flights were expected to use both stages of the Big Falcon Rocket (BFR) rocket, since evolved and renamed to the Starship spacecraft and Super Heavy booster. In 2019, Musk revealed that these suborbital flights could instead utilize only the Starship vehicle with no booster, achievable for distances of approximately 10,000 kilometers or less. In order to meet thrust requirements, a single stage suborbital Starship would include an additional two to four Raptor engines.

Given the inherent danger of rocket powered space travel, the Starship system will complete many, possibly hundreds of flights before flying passengers, with the first Earth to Earth test flights beginning as early as 2022.

Another side effect of the Starship Mars architecture, which requires that methane be captured from Martian resources to refuel spacecraft and return to Earth, is that the same propellant production processes can be used on Earth to make Starship operations carbon neutral.

The idea of carbon neutrality, removing as much carbon from the atmosphere as is emitted by the system, is a crucial part of ensuring that future transportation systems do not contribute to the harmful effects of climate change. Musk has confirmed that carbon neutrality is an important goal of the Starship program.

SpaceX is not the only major commercial spaceflight company with a suborbital transportation concept. Richard Branson’s Virgin Galactic also has a vision of space travel around Earth. SpaceX’s Crew Dragon flying astronauts to Low Earth Orbit, and Virgin Galactic’s SpaceShipTwo flying crew on suborbital trajectories above the official American boundary of space at 80 kilometers altitude, are the only two commercial companies actively flying humans to space today. A successor to SpaceShipTwo is planned that could provide trans-continental spaceflights for passengers.

While no technical details of a “SpaceShipThree” have been announced by Virgin Galactic, it is fairly likely that the vehicle would be air launched, similar to the SpaceShipOne and SpaceShipTwo suborbital spaceplanes. SpaceShipThree was originally intended to be a orbital vehicle, developed jointly by Virgin Galactic and Scaled Composites.

Scaled Composites was the manufacturer of SpaceShipOne, the first private crewed spacecraft which won the Ansari X Prize by completing two crewed spaceflights using a reusable spacecraft in 2004. Scaled Composites also built the first SpaceShipTwo, the VSS Enterprise, as well as the WhiteKnightTwo carrier aircrat VMS Eve, before jointly founding The Spaceship Company with Virgin Group. Scaled Composites is now a wholly owned subsidiary of Northrop Grumman, and The Spaceship Company currently manufactures SpaceShipTwo vehicles for Virgin Galactic.

While the name SpaceShipThree has not been mentioned recently, plans for a suborbital point-to-point transportation system are still planned by Virgin Galactic. Branson has mentioned a successor to SpaceShipTwo that can provide trans-continental spaceflights as recently as 2019. No timeline for test flights or commercial operations with this system have been announced yet.

For both of these systems, it is possible that suborbital cargo transportation could precede passenger flights as a way of proving the reliability of the vehicles. One company has no intention of flying people, but is pursuing suborbital spaceflight as a cargo transportation market: the smallsat launch company Astra.

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Astra recently launched their second orbital launch attempt, Rocket 3.2, which came up just short of achieving orbit for the first time in Astra’s history. The company is expected to achieve orbit with a paying customer payload on board Rocket 3.3 in 2021.

For suborbital transportation, Astra has proposed an upgrade to the Rocket 3 family, named Rocket 5. The first stage of Rocket 5 would be identical to that on Rocket 3. The second stage would be similar to the first stage, except with a single engine instead of five. The final stage of Rocket 5 would be the same as Rocket 3’s upper stage. This vehicle could be available for suborbital cargo deliveries no earlier than 2022.

The Competition: Supersonic Airliners

While multiple suborbital transportation concepts proceed through development, several supersonic aircraft designs are also expected to debut, creating competition for the market of high speed transportation around the planet.

One such entrant is Boom Supersonic, which rolled out the XB-1 prototype aircraft in November 2020. The XB-1 will reach supersonic speeds during test flights which will inform the design of a supersonic airliner named Overture. Flight tests are expected to begin in 2021 in Mojave, California. The XB-1 has three General Electric J85-15 engines, from the same family of engines which power NASA’s T-38 Talon training aircraft and powered the WhiteKnightOne carrier aircraft which air-launched SpaceShipOne.

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The Overture airliner is planned to roll out by 2025, and be operational by 2029, carrying up to 88 passengers at ranges up to approximately 7,870 kilometers. The aircraft will be powered by a to-be-determined engine provided by Rolls-Royce. Both the XB-1 test program and the Overture airliner are planned to be carbon neutral.

Orders for the Overture from both Japan Airlines and the Virgin Group have been announced. It is unclear whether the Virgin Group orders are from Virgin Galactic, who did enter a partnership with Boom on Overture in 2016, or possibly the Virgin Atlantic airline.

Despite having their own suborbital design concept, Virgin Galactic is involved in the supersonic airline effort. While their partnership with Boom has not been promoted by either company recently, Virgin Galactic unveiled a partnership with Rolls-Royce for a Mach 3 capable aircraft in August 2020. The aircraft would have a passenger capacity of up to 19 people.

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Another offeror in the market is Aerion Supersonic, developing their AS2 Supersonic Business Jet. Aerion recently broke ground on a new headquarters at Melbourne International Airport, just south of the Cape Canaveral Space Force Station and Patrick Space Force Base on Florida’s space coast.

The AS2 jet is a partnership with Boeing and General Electric, and is designed to carry up to 10 passengers at speeds up to Mach 1.4 over open water. The AS2 would be flown closer to Mach 1.2 near land to mitigate the intensity of sonic booms, or subsonic if required. Historically, disturbances on the ground from sonic booms have contributed to the retirement of Aérospatiale and British Aircraft Corporation’s Concorde and the hesitation from other companies to pursue supersonic air travel.

Technical and Financial Challenges

The ideas of hypersonic suborbital space travel and subsonic atmospheric flight vary in their approaches to a similar problem, but also face some common challenges. Both methods do produce sonic booms, which can disrupt people living on the ground and, in extreme cases, cause damage or injuries. Supersonic aircraft produce sonic booms along the entire flight path, with varying intensities depending on speed, altitude, and the geometry of the aircraft. Rockets, on the other hand, only cause sonic booms to be heard during landing, as the shockwaves created during launch move upwards, away from any observers that could hear them.

In order to better understand the effects of sonic booms from aircraft, Lockheed Martin’s Skunk Works division is developing the X-59 QueSST (Quiet Supersonic Technology) for NASA’s Low-Boom Flight Demonstration Program. The X-59 is uniquely shaped to decrease the intensity of the supersonic shockwave so as not to disturb populated areas while flying overhead.

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owered by a General Electric F414 engine, the same as is used in the Boeing F/A-18 Super Hornet fighter jet, Lockheed Martin test flights are scheduled to begin in 2021, followed by delivery to NASA in 2022. The goal of the Low-Boom program is to collect data on the volume of sonic booms in order to inform legislation on approving supersonic air travel over populated areas. X-59 flights to contribute towards this mission begin in 2023, in addition to flights already underway using NASA’s F/A-18 fleet.

Sonic booms are not the only noise concern with these new methods of travel. Rockets produce potentially dangerous noise levels during launch, especially those on the scale of Starship. SpaceX plans to solve this by launching and landing far offshore from population centers, which means using a slower form of transportation to travel between the spaceport and the destination city.

Large rockets like Starship, especially if the Super Heavy booster is used, also have large blast danger areas in the event of a catastrophic anomaly while fully fueled. However, before flying commercial passengers, the Starship system will need to prove reliability comparable to that of present day airliners. This will surely include demonstrating a negligible risk of such an anomaly occurring. The Starship launch system also has no in-flight abort capability in the event that the Super Heavy booster or Starship’s Raptor propulsion system fails during flight, a risk that will need to be retired by flying many missions with only cargo on board, including both space missions and Earth to Earth test flights.

Another safety advantage winged aircraft have over propulsively landed rockets is the ability to glide in the event of an engine failure. Both these new supersonic airliners and spaceplane concepts like SpaceShipThree would be able to glide towards a controlled emergency landing during an emergency. This was recently demonstrated during Virgin Galactic’s most recent SpaceShipTwo flights, when VSS Unity glided back to the runway at Spaceport America after aborting during engine ignition. Vehicles which rely on their engines to land safely, such as Starship, do not have this contingency.

Looking past the important but solvable technical issues, the business case for faster Earth travel also remains to be proven. The costs of space launches and the limited capacity on upcoming supersonic airliners will likely mean higher ticket prices than today’s subsonic aircraft. The appeal of shorter travel times will need to outweigh the increased price.

An aspect of tourism may also come into play, as some travelers book travel not as commuters, but just to experience high speed air travel or suborbital spaceflight. However, this brings in even more competition from systems designed for suborbital space tourism, such as Blue Origin‘s New Shepard rocket or Virgin Galactic’s own SpaceShipTwo. Orbital space tourism on board SpaceX’s Crew Dragon and Starship vehicles may also draw customers away from the suborbital options.

Suborbital spaceflight offers faster travel times than supersonic airliners, arriving anywhere on Earth in under an hour versus a couple hours on an aircraft. But space travel also offers additional challenges for safety and for noise levels on the ground. The key to systems like Starship being successful for Earth to Earth transportation will be proving the same level of safety as an airliner. If this can be done, than a combination of spaceflight and high speed airliners may be the future of travel around humanity’s home planet.

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#2 2020-12-31 15:39:18

kbd512
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Registered: 2015-01-02
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Re: Coast to Coast starship flights

Starship will never compete with a purpose-built supersonic airliner on cost.  The difference in fuel consumption rate is far too great to make Starship as economical to operate, and it uses 6 engines.  A supersonic airliner has two to four engines, at most.  Let's not pretend that turbo pumps running at 300 bars of pressure will be as trouble-free as a non-afterburning low-bypass turbofan operating at a fraction of that pressure, either.  The dry mass fraction of that airliner is also lopsidedly in its favor to boot.  Starship is very cheap to build, but it won't be any cheaper to operate unless it uses atmospheric O2 to supply some of the oxidizer.  If it did that, then the engine is no longer a Raptor and the airframe is no longer a Starship airframe.  Starship can seat as many passengers as the A380, but that's still not enough to overcome its fantastic fuel burn.

Boom can do New York to LA in 2.5 hours.  It would take at least 1 hour to load and 1 hour to unload a full complement of passengers from a vertical launch vehicle like Starship, and at least that long to load 1,200t of propellants, so irrespective of whether or not you fly 5 times faster, Boom already beat you on trip time, it burned a lot less gas to do it, and it can land on any standard runway airport runway in the Western Hemisphere without issue.

If you were talking about New York to Tokyo, that's a different story.  Starship could easily beat any intercontinental airliner's travel time, even a supersonic one, by a lot.  Those flights only take place a few times per day, at most.  If you have the cash to pony up for an expensive but fast flight, then it might make sense.  Everyone else will still be flying on subsonic or supersonic but comparatively fuel-miserly airliners that use moderately high cruising altitudes and aerodynamic lift.

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#3 2021-01-01 10:04:28

louis
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From: UK
Registered: 2008-03-24
Posts: 6,308

Re: Coast to Coast starship flights

There are definitely huge challenges to be faced. But I think you are being too negative about the potential of a Starship E2E craft.

Regarding loading of passengers I would see that being much quicker than with an airline with people entering at mutiple levels.

The cost of fuel burn will easily be covered by what will essentially be business and luxury class travellers.

The footprint of the craft on the ground is much smaller. You don't have to build and maintain huge expanses of tarmac and hangars. You do have to get your passengers to the offshore Spaceport some 15 miles offshore.  Drone craft might be the simplest solution. They could land right in the middle of cities on adapted high rise rooftops.

kbd512 wrote:

Starship will never compete with a purpose-built supersonic airliner on cost.  The difference in fuel consumption rate is far too great to make Starship as economical to operate, and it uses 6 engines.  A supersonic airliner has two to four engines, at most.  Let's not pretend that turbo pumps running at 300 bars of pressure will be as trouble-free as a non-afterburning low-bypass turbofan operating at a fraction of that pressure, either.  The dry mass fraction of that airliner is also lopsidedly in its favor to boot.  Starship is very cheap to build, but it won't be any cheaper to operate unless it uses atmospheric O2 to supply some of the oxidizer.  If it did that, then the engine is no longer a Raptor and the airframe is no longer a Starship airframe.  Starship can seat as many passengers as the A380, but that's still not enough to overcome its fantastic fuel burn.

Boom can do New York to LA in 2.5 hours.  It would take at least 1 hour to load and 1 hour to unload a full complement of passengers from a vertical launch vehicle like Starship, and at least that long to load 1,200t of propellants, so irrespective of whether or not you fly 5 times faster, Boom already beat you on trip time, it burned a lot less gas to do it, and it can land on any standard runway airport runway in the Western Hemisphere without issue.

If you were talking about New York to Tokyo, that's a different story.  Starship could easily beat any intercontinental airliner's travel time, even a supersonic one, by a lot.  Those flights only take place a few times per day, at most.  If you have the cash to pony up for an expensive but fast flight, then it might make sense.  Everyone else will still be flying on subsonic or supersonic but comparatively fuel-miserly airliners that use moderately high cruising altitudes and aerodynamic lift.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#4 2021-01-01 15:40:24

kbd512
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Re: Coast to Coast starship flights

Louis,

To be perfectly frank, electric airliners are much closer to engineering reality than a hypersonic rocket-powered VTOL airliner.  I'm only pointing out that the "huge challenges" faced are fuel burn rate, engine count, inert mass fraction (which determines vehicle durability), and passenger evacuation are intractable problems.  Rocket engines aren't going to become more fuel efficient unless they're no longer rocket engines, the engine count is what provides the necessary thrust to lift off to begin with, and the inert mass fraction is driven by the need for nearly all of the vehicle's weight to be propellant.  Since you're not going to reduce the fuel burn rate, use fewer engines than needed to get off the ground, nor change the fact that Starship would be an airliner sitting on its tail, I don't see how this will ever be practical.  It may be technologically feasible if every flight is perfectly executed, but no such success rate, relative to conventional airliners, has ever been demonstrated with rockets.  Individual jet aircraft have performed more power cycling associated with takeoffs and landings in a single day than any rocket engine has ever demonstrated in terms of total engine starts / stops.

Beyond that, all of those airport runways have already been paid for.  A Starship would require a large exclusion zone beyond the tiny pad footprint so that accidents don't throw shrapnel into homes a mile away, so the small size of the landing pad is another moot point.  When landing, there's no such thing as "line up and wait" with a rocket, either.  If one of these things ever crashes and throws debris onto the next closely-spaced landing pad, is the next inbound pilot supposed to land in a flaming wreckage pile?  No significant diversion is possible unless you're very high in the atmosphere.  These VTOL rockets come down like meteors.

If that wasn't enough, the window-destroying sonic booms would prevent it from ever diverting to alternate landing pads that aren't far away from population centers.  That was the entire point of Boom, and one of two reason it's fundamentally "different" from Concorde.  The other reason is a remarkable reduction in fuel burn, relative to lighting afterburners, which Concorde had to do to fly at Mach 2.  Boom changes "the sonic boom" into an acoustic wave form that doesn't trash windows or otherwise scare the crap out of people on the ground.  It sounds like a deep rumble, rather than the thunder that follows a lightning strike.  For various reasons, that's impractical for Starship.  Starship will never pass noise abatement ordinances on account of the fact that it's powered by six of the most powerful rocket engines on the planet.

Anyway, the military would probably have some kind of use for it, but they won't be going supersonic over CONUS with it, in the same way that existing regulation forbids them from breaking Mach unless there's some kind of inbound military threat.

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#5 2021-01-01 16:06:33

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 21,860

Re: Coast to Coast starship flights

Even the reliable Falcon 9 gets flight delays
https://spacenews.com/back-to-back-laun … rate-musk/

These were 2 ships in a 36 hours of each other
.

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#6 2021-01-01 18:24:06

tahanson43206
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Registered: 2018-04-27
Posts: 5,773

Re: Coast to Coast starship flights

For SpaceNut re #5

It's going to be difficult to keep this topic on a narrow focus.

I went back to be sure, and you started this topic.

Since you introduced the link in #5, I feel free to report my impressions .... the proposed flight rate of 48 for 2021 is typical Musk, but apparently the Air Force has an identical target for one of their ranges, so there may be some momentum building for that to happen.

Meanwhile, Gwynne Shotwell offered a caution about some of the numbers forecast for the near term.  She said SpaceX is reserving on the high side so they don't unnecessarily short themselves, but readers/viewers should not assume SpaceX actually intends to meet the targets.

I think you're going to have a challenge keeping this topic on track.

Continent to Continent might make sense, as kbd512 pointed out.

I simply don't see the point of flights for such short distances.  The entire world is moving towards Zoom visits (and the enterprise scale equivalent).  There is less and less need for people to physically travel for business. 

(th)

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#7 2021-01-01 19:43:29

kbd512
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Posts: 4,197

Re: Coast to Coast starship flights

tahanson43206,

Actually, I think we are narrowly focusing on a practical coast-to-coast high speed transport, but Starship doesn't fit the description of a machine suitable for that purpose, since it was always intended to be the upper stage of a two-stage-to-orbit super heavy lift rocket, not an airliner.  If Starship carries 600 passengers, then each passenger has to pay for 2,000kg of LOX/LCH4.  The actual cost differential is nominal, in the grand scheme of things, yet major airline services would laugh at paying for so much fuel per passenger-mile.

A Boeing 747 carrying 500 passengers (these jets can also carry up to 600 people) burns approximately 0.01 gallons of Jet-A per passenger, per mile.  New York to LA is 2,451 mile flight, so 24.51 gallons ($98.04 per person at $4/gallon of Jet-A) of fuel per person to travel from coast to coast at 550mph.  We retired all 747s from passenger carrying service because those jets burned a little bit more fuel than twin-engined 767 / 777 / 787 jets.  The new GE90 engines that power the 787 were STILL not efficient enough to be to the airline services' liking, so then GE developed the GE9x series of engines and Rolls Royce upgraded the Trent series, which are just now entering service.  The 787-9, which is far easier to completely fill up with passengers on every flight, is effectively a 100mpg airplane, whereas the venerable 747-8 is a "paltry" 89mpg airplane.  All fuel has to be created / delivered / stored.  The new GE9x engines would make the 787 a 110mpg airplane.  Starship will be burning 400kg of LNG (~$230 per person at $575/t, plus $26 for the 1,133kg of LOX, at $0.1/gallon), per person to make the same trip, or 6.1275kg (3.87 gallons, per person, per mile), or 252.6 gallons per person for the trip, which makes it a 9.7mpg "airplane" (rocket).  My 2017 Cadillac Escalade is 22mpg on the highway.  Since Boom is going twice as fast as a 787, it will burn twice as much fuel, becoming a 50mpg airplane.  That's about the limit of tolerable per passenger per mile cost to the major airline services.

If you look at the fuel economy figures for airliners, you can see that the thirstiest small turbofan short haul jets are 50mpg or better:

Fuel economy in aircraft

All of the long haul machines meet or beat any land-based hybrid vehicles for fuel economy.  Engine wear-and-tear, plus fuel economy, equals operating cost.  A pilot's hourly wages are a small fraction of what the airliners pay to run their businesses, so fuel burn and engine maintenance is what drives the feasibility of every new airliner that enters service.  Each successive generation of aircraft consumes less fuel on a per passenger-mile basis, to the point that the airlines expect 50mpg to 100mpg performance from all new jets, but want "better still".  I can only speak for myself when I say that any jet I fly on will have a pair of fully qualified pilots in the cockpit, but we're going to need a pair of space flight qualified pilots for Starship.  I wager those pilots will also want more money, on account of their impeccable qualifications and the fact that space flight is inherently more dangerous than ordinary atmospheric flights.  If that wasn't enough, where are you going to find enough "rich people" to pay $250 for gas, plus the maintenance costs associated with operating 6 of the highest performance rocket engines ever made?  Costs don't go down as performance goes up, they go shooting off into the stratosphere like a proverbial rocket engine.

You'd be lucky to fill up 2 flights per day between major cities, yet passengers and therefore airline services balked at paying the fuel bill for the 747s and A380s, which is why we have 787s and A330s.  We can routinely fill 200 to 300 seats far more easily than 600 seats.  If the AGA33 concept ever sees the light of day, we're easily talking about a 250mpg airplane and nominally longer intercontinental flights that afford far more room to each passenger (the only real complaint passengers have with modern subsonic jet aircraft), and the Celera 500 proves that it's feasible to achieve 737 flight speeds with diesel engines and propellers while burning 8X less fuel.  The all-electric Ampaire TailWind will make most short haul flights even more fuel efficient than that.

So, no, the idea of flying a Starship coast-to-coast is just crazy talk.  LA to Tokyo, non-stop, in a few hours, is a far more compelling argument.  That kind of time savings is worth the additional cost to some people who need to get from Point A to Point B very quickly, because time is money in business.  We simply can't turn around one of these steel Leviathans in the time frame required to make shorter flights practical, and SpaceX is already paying for a standing army to support commercial and exploration space flight objectives.  Having too many irons in the fire makes servicing all of the irons impossible.  The mission statement of SpaceX is developing the technology required to explore space and colonizing other planets, not transporting rich kids from city to city in extravagant fashion.  We already have private jets and limos for that.

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#8 2021-01-01 20:16:34

tahanson43206
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Registered: 2018-04-27
Posts: 5,773

Re: Coast to Coast starship flights

For kbd512 re #7

This topic provided an opportunity for saving valuable insights for anyone who comes across the topic later.

SpaceNut ... After reading kbd512's multiple posts on this subject, I finally went back and read the original article you cited in Post #1

The article contains many of the points kbd512 made.  I'm assuming kbd512 did not read the article, but instead was writing from his own knowledge and experience.

The article itself did NOT mention coast to coast Starship flights, or if it did, I sure missed it.

it's probably too late to change the topic title ... I think it would have survived longer as "Continent to Continent Starship flights"

As it is, this topic may have reached it's zenith.  Hopefully it will land safely.

(th)

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#9 2021-01-01 20:17:10

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 21,860

Re: Coast to Coast starship flights

Seems under very unusual conditions would a Starship be called for or wanted for passengers.

Would that also hold true for cargo?

One could look at NY to France as being about the same as LA but going to Japan would be where it might excel. The trouble is you are looking for a use for an existing vehicle which is one of the problems for the slab.

There as others in the first post to analyze as well not just starship.

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#10 2021-01-01 23:14:22

kbd512
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Registered: 2015-01-02
Posts: 4,197

Re: Coast to Coast starship flights

tahanson43206,

Sorry, but I did not read the article.  I'm using what I know about what things cost, what people are willing to pay, therefore what's practical and what's not.  I don't need to read a news articles to tell me what I already know.  I did some basic math using freely available information on the cost of Jet-A / LOX / LCH4 and fuel burn rates.  That told me pretty much everything I needed to know about the practicality of making New York to LA flights using the upper stage of a super heavy lift launch vehicle.

Nobody has done this yet because it's not feasible to do it with current technology.  We have greatly improved aerodynamics (thanks to CFD optimization software), decreased structural weight of airframe materials (CFRP), and turbofan engine efficiency (high pressure ratio, ultra-lean burn at blow torch temperatures) to the point that a purpose-built turbofan (like the F-136 engine with ADVENT technology that wasn't quite ready for prime time when the F-35 program was in initial development) can burn about twice as much fuel to go about twice as fast as a subsonic airliner.  Whenever you start trying to fly appreciably faster, aerodynamic heating rapidly increases airframe weight (CFRP and Aluminum won't cut it, so you'll need stainless steel), thus the lift-to-drag (bigger wing generating more induced drag to carry the increased weight of steel) and therefore thrust requirement (more thrust to overcome more drag), thus engine efficiency (at low to moderate subsonic speeds pistons or turboprops are most efficient, at high subsonic speeds turbofans become more efficient, the fan in a turbofan starts becoming an aerodynamic equivalent of a brick wall around Mach 3, so turbojets tend to get used for efficiency at Mach 2.5+ speeds, then ramjets start looking more attractive around March 4 or so, and by Mach 10 or so, even scramjets become impractical, so you switch to using rocket engines), and then fuel burn really starts to "take off" (the faster you go, the more fuel you need to burn).

There's never been a shortage of people willing to blow mad money on impractical ideas.  I still think supersonic jets are playthings for rich people, but the relative fuel burn associated with a modern Mach 2 airliner design is no worse than a small business jet, on account of how business jets are made (generally from heavier but cheaper Aluminum alloys, rather than carbon fiber tape layups that airliners have mostly switched over to using these days) and the poor fuel economy of very small turbofans (biz jets) vs very large turbofans (intercontinental airliners).  There might be an engineering reason why modern turboprops typically start around 550hp and go up from there- just sayin.

This kind of stuff falls squarely in the same realm as all of us cruising around in "flying cars" like the Jetsons without any pilot training or Star Trek level technology.  It's fun to fantasize about, but when the rubber meets the road, it's absurdly impractical using current technology, with a total lack of pilot training.  The entire reason air travel is so much less dangerous than highway driving is specifically because far fewer vehicles are present in far more physical space and most of the pilots at the controls have better training, recurring training, lots of experience flying, and better awareness of what's going on around them.  Computers are a valuable aid in that cause, but not the primary reason why the overwhelming majority of airliners make it to their destination in one piece.  If NHTSA mandated the use of multi-million dollar driving simulators to train new drivers, recurrent qualification to maintain a vehicle operator's permit, drug testing, yearly medical screenings, and licenses that can be revoked at any time without the need to obtain court orders, does anyone here believe we'd have a fraction of the motor vehicle accidents?  Any significant mistake you make at the controls of an aircraft, and you will find yourself talking to a FAA rep who will determine on the spot whether or not you keep your license, because they exist to maintain the confidence of the flying public in their ability to evaluate and regulate every aspect of flying, with a keen eye towards absolutely minimizing the number of aviation related accidents.

Anyway, it's a cool concept that's also totally impractical, even if you can technically make it work, which has yet to be proven.  After I see several hundred successful orbital flights, which include 24 hour or less turnaround times, then we can reevaluate the practicality of hypersonic point-to-point travel.

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#11 2021-01-02 13:09:23

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,363
Website

Re: Coast to Coast starship flights

Transport of people and/or cargo over long distances by air has a price that depends mostly upon speed,  with reusability and reliability both huge factors in that price.  Rocket mail was attempted in Germany before WW2,  but reliability,  not the nonreusable costs (which were considerable),  killed it.

The standard today for comparison is long range transport with high-subsonic gas turbine-powered airplanes.  That's for both people and cargo.  It takes 12-14 hours to cross the northern Pacific this way,  a little longer to reach Australia from North America,  which is essentially the antipodes.

A supersonic transport can do this with a lower transit time,  but a higher cost.  That is inevitable,  because drag forces are inherently higher in supersonic flight,  as compared to subsonic flight,  almost no matter what design innovations you might have.  The wind pressures are just greatly higher.  You have to burn fuel to overcome drag in steady-state flight,  no matter what. 

Similarly,  the engines suitable for supersonic flight inherently have lower bypass ratios than engines that only fly subsonically.  There are no innovations to get around ths,  only those which affect the precise numbers.  But supersonic bypass ratios are,  always have been,  and likely always will be,  lower than subsonic bypass ratios.  The thrust specific fuel consumptions are inherently higher at low bypass ratio.  There is no way around that,  so there will always be a higher fuel burn in supersonic flight.

The faster you intend to fly supersonically,  the higher the drag (and resulting fuel burn),  more-or-less quadratically increasing with speed.  The shorter your flight time will be,  only linearly changing with speed.  Those physics plus the bypass effect on engine efficiency,  are why all forms of supersonic flight with (reusable) airplanes has always been far more expensive than subsonic flight.  It will likely remain that way,  no matter what innovations get introduced. Those only affect how strong a quadratic model you have to use.

There is a second complicating issue that increases very greatly the costs of supersonic flight,  and that is friction aeroheating,  also greatly (and nonlinearly) increasing with increasing supersonic speed.  Organic composites are ruled out for steady flight by equilibrium skin temperatures somewhere near Mach 1.5-1.7.  Aluminum is ruled out by around Mach 2.2-2.4.  Titanium is ruled out above about Mach 3.8 to 4.  That leaves you stainless and alloy steels,  and dense ceramics.  Both are heavy,  and that increases fuel burn due to weight.

My understanding of the organic composite Boom Supersonic prototype (and related ultimate design) are that they never fly faster than about Mach 1.3-1.4.  The high strength/weight organic composites simply do not allow faster flight in the face of the aeroheat risks.  The lower supersonic speed and composite construction to save weight,  plus the better engine technology available today,  is EXACTLY how they get the cost down to something perhaps affordable.  You can cut about 1/3 off your flying time,  for only a somewhat-higher ticket price,  compared to a subsonic transport. 

Transoceanic rocket transport avoids much of the aeroheating problem by going exoatmospheric,  and doing the reentry as a transient,  fundamentally-heat-sinking problem,  at flight's end.  Just as we have done with reentry for about 66 years now.  That kind of transient heat protection problem is vastly different from the steady atmospheric flight heating problem.  It is far easier,  less expensive,  and lighter in weight to solve.

If the rocket really is reusable,  then the main cost factor is the truly enormous propellant burn required for rocket travel at all.  The ticket price will always be higher than subsonic air travel ticket prices,  that is inherent.  It will likely be higher than ticket prices for modest supersonic air travel (that being under Mach 2 at most,  and more likely under Mach 1.5 to use composites).  It just gets down to the question of how much more are you willing to pay for cutting transoceanic travel time drastically (from a dozen hours to under half an hour)?

We've tried supersonic travel once before with Concorde at Mach 2.  That was with much poorer engine technology,  using an aluminum and titanium airframe.  (The Boeing Mach 3 design that was never built,  was a heavier all-titanium airframe.)  Concorde cut times roughly in half.  But it was not really a commercial success,  because it was only a niche market due to its cost.  Slowing down to Mach 1.3-1.5,  with far better engines,  and a composite airframe,  might be a lot more attractive,  even though you only shave off about a third of flying time. We'll soon see,  I think,  thanks to Boom Supersonic and maybe a few others.

Whether drastically shaving flying time at a much higher price yet,  with rocket travel,  will prove commercially attractive is something we might actually learn if Musk is successful.  I think the answer is still way far out in the future on that.  I suspect it's a niche market only. But maybe we'll see.

GW

PS - most people do not know the real genesis of the Saturn 5 rocket design,  done by Von Braun for US Army at Huntsville,  AL.  That was only a paper design until NASA "bought" it (and him) for its Apollo effort.  It was originally a rocket travel troop transport,  one-way to Russia with about 100 men per rocket. The "third stage" was the troop transport lander. 

NASA had him replace that with a real propulsion third stage to be its Saturn 5 moon rocket.  This stuff actually was published as "gee look how good we are" ads in the predecessor to "Aviation Leak" magazine in the late 1950's and early 1960's.

PPS- most people also do not know that the original Apollo design landed the entire Apollo CM/service module on the moon.  It took two Saturn 5 launches per moon mission to do this,  refuelling in LEO from one to the other,  in order to send this cluster direct to the moon. 

The idea of lunar orbit rendezvous using a separate lander came from outside NASA,  meeting very heavy "not invented here" resistance from NASA.  Only the pressure of beating both the Russians,  and JFK's timeline,  forced them to adopt it.  Which got them down to one Saturn 5 per moon trip.  Which was something they could afford,  and that both Congress and the public would buy.

Last edited by GW Johnson (2021-01-02 13:30:40)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#12 2021-01-02 19:23:45

kbd512
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Re: Coast to Coast starship flights

GW,

If any part of this persistent claim of yours was actually true, then there's no way that fighter jets like the F-35 and F-22 wouldn't suffer from catastrophic structural failures, nor would any supersonic radar-equipped fighter or bomber with a fiberglass nose radome survive, for that matter.  The stripped-down F-22 test articles could and did super cruise above Mach 2 for extended periods of time, meaning longer than 30 minutes.  None of them suffered from catastrophic structural failures, and nearly the entirety of their skin and leading edges were radar-absorbing structural composites using epoxy and glass or carbon fiber.  The skin temperature of the Concorde was 100C at Mach 2, 120C at Mach 2.2, and 150C at Mach 2.4.  That falls very well within the temperature limitations of high temperature epoxies, some of which maintain enough bond strength to operate up to 300C.  The epoxies that are available today are not the same as whatever was available in the 1970s.

Considerations of failure mechanisms in polymer matrix composites in the design of aerospace structures

Boom has already stated that the fastest speed they can achieve over land is Mach 1.4, due to not being able to pass noise restrictions regarding sonic booms.  The speed restriction has nothing whatsoever to do with the structural integrity of the airframe or epoxies used in CFRP.  We have epoxied composites that retain more tensile strength at elevated temperatures, up to consumer oven temperatures, than Aluminum does.  The epoxies that can do that are really expensive, but readily available as commercial products, and are made by the likes of 3M (ScotchBond), Loctite (Hysol), Cotronics (DuraBond), and others, specifically for use in both civil and military aircraft, as well as structural composite parts used near engines or high-heat / high-pressure industrial applications.

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#13 2021-01-03 00:02:56

GW Johnson
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Re: Coast to Coast starship flights

Kbd512:

A quote from the article you linked:

"However, as the skin temperature rises to 120 °C or above, thermo-oxidative degradation and its potential consequences can either prevent composites from being used at all or require them to be protected – usually through insulative layers – such that they operate at more benign temperatures. In many cases, the use of insulation is not permissible (such as on aerodynamic surfaces or parts exposed to high-speed airflow), but, recently [50, 51], some development on thin thermal-barrier coatings has been done to try to address this problem. The goal of thermal barrier coatings is to reduce the temperature of the substrate such that it operates at a more benign temperature where it is stable."

120 C as listed in the article equates to 248 F.  That's right in the same ballpark as the failure temperature rule-of-thumb (290 F) that we used for military-grade asbestos-epoxy cement within rocket motors at the rocket plant.  It failed by ceasing to be epoxy:  it pyrolyzed into carbon char.  The resulting char was relatively worthless at binding the asbestos fibers together.  It was no longer structural once that happened. 

The "bond strength at 300 C" (572 F) that you quoted is the shear strength of char still holding things together after the epoxy has long "died",  and it is NOT a large number,  said char resembling the charcoal in your BBQ grill. Most epoxy-type composite materials need to stay under about 250-300 F to maintain some structural strength,  and are usually pyrolyzing into char above 300 F. There may be some that can go somewhat higher,  but not 300 C = 572 F.  Not and stay epoxy. There is a huge difference between one-shot use and usable-repeatedly.

The stuff I quoted,  which you had a problem with,  was for material soaked out to the full recovery temperature of the adjacent air,  which is very nearly the total temperature of the adjacent air.  Materials WILL soak out that hot,  if aeroheated without any paths to cool by conduction,  and without any significant emissivity for cooling by re-radiation to the environment.  That's just heat transfer physics,  you cannot argue with that. 

In aircraft structures,  the paths for conduction into interior items are usually few and far between.  Skin panels are usually relatively isolated in that respect.  So unless there is some kind of active cooling designed-in (and usually there is not),  that kind of conduction is not a significant cooling path. 

In aircraft structures,  the surface coat texture and color drastically influence the thermal emissivity that controls re-radiative cooling.  Dark or black surfaces,  especially those not smooth and shiny in texture,  usually (but not always) have rather high emissivities,  usually at or above 80%.  Shiny surfaces and white or light paint colors usually (but not always) have low emissivities,  usually under 20%.

This is quite important to radiation physics,  because heat flow rate per unit area is proportional to emissivity,  and proportional to the difference of two temperature-to-the-fourth-power terms.  One is the material equilibrium temperature ^ 4,  the other is the effective environmental temperature ^ 4 (said temperature usually taken to be 300 K). 

Skin panels with high emissivity can reradiate and stay cooler than the recovery temperature of the adjacent air,  which is the driving temperature for the aeroheating to the panel.  Skin panels that cannot effectively re-radiate because of low thermal emissivity will essentially soak out to the air recovery temperature.  The equilibrium panel temperature reflects the balance between heat flow inputs and outputs,  to and from the panel. Physics.

That re-radiative cooling mechanism is EXACTLY how the skins on the jets you named stayed cool enough not to fail,  at the speeds you indicated. Camouflage coatings are usually high emissivity. And that is usually specified by contract. The equilibrium temperature can be quite a bit cooler than the recovery temperature,  especially for emissivities of 80% and above. 

The lack of that same cooling mechanism at low emissivity is why skin panels on the Concorde were 100 C (212 F) at Mach 2 in the stratosphere.  The standard-day total temperature for Mach 2 flight in the (cold) stratosphere is 242 F = 117 C.  Recovery would be a tad lower:  just about 212 F = 100 C.  Those were shiny aluminum skins with near-zero thermal emissivity.  No surprises there.

Most of the radomes I was familiar with,  those that were capable of sustained supersonic flight,  were simply not fiberglass or epoxy composites.  There are a number of specifically-developed radome materials for supersonic application.  Some will go faster than others.  But they are NOT epoxy composites,  unless your speed is rather low supersonic or less. Both the aircraft and the missiles use the same technology.

Some of the material designations I found in AD-A007956 "Avionic Radome Materials",  authored by R. H. Cary (for a NATO/AGARD document) are "alumina",  "pyroceram",  "silica",  "cordierite" = "rayceram",  "silicon nitride",  "boron nitride",  and "beryl oxide".  These are nearly all ceramics of one kind or another,  listed in multiple forms in the document.  Some are reinforced with ceramic fiber or fabric.  The missiles usually use the silicon nitride or pyroceram materials.  Some of those (like Phoenix) peaked briefly at Mach 5,  but were significantly supersonic all the way to target. 

For lateral skin panels,  the key to success is re-radiative cooling.  That's how you get away with aluminum panels past Mach 2.2 in the stratosphere.  It's how you get away with epoxy composites past Mach 1.4-ish in the stratosphere.  It's how you get away with titanium past Mach 4 in the stratosphere.  Etc.

The aeroheat rates are order-of-magnitude worse at stagnation points and lines.  That's why the nosetip and leading edge problems are harder to solve.  But you use the same basic mechanisms:  primarily re-radiative cooling,  plus significant conduction from the stagnation line into more aft regions where the aeroheating is lower,  using the attach structures for the leading edge parts as your conduction paths.  You can still avoid active cooling by doing that,  for any practical supersonic jet aircraft design. 

You can even add some heat-sinking to go hypersonic,  as long as that is a short transient,  not steady-state. That's how the missiles get away with going that fast.

GW

Last edited by GW Johnson (2021-01-03 00:06:57)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#14 2021-01-03 04:57:32

kbd512
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Registered: 2015-01-02
Posts: 4,197

Re: Coast to Coast starship flights

GW,

Apart from active cooling using the fuel, supersonic stealth aircraft have thermal barrier coatings on them to protect against radiant heat.  They're also used in racing.

The following link shows what a blow torch does to a protected vs unprotected carbon fiber composite:

Ceramic Coating of Carbon Composite Heatshield -Zircotec ThermoHold Ceramic Coating Thermal Barriers

Incidentally, this is how F1 teams prevent hot engine exhaust headers from pyrolyzing their carbon fiber chassis.  The ceramic thermal barrier coating is applied to both the composites and the exhaust headers to keep under-cowl temperatures manageable.

The point is, it's doable, its been done for some time now, and it obviously works well.

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#15 2021-01-03 12:39:00

GW Johnson
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From: McGregor, Texas USA
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Posts: 4,363
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Re: Coast to Coast starship flights

Interesting demonstration.  Looks like the ceramic coating does help quite a bit.  Move the torch closer,  and both fail,  the unprotected sooner,  I would think.  These technologies are effective,  but also more limited in what they can do,  than most people are led to think.  That just advertising overstatement.   

What I was involved with,  in the rocket and ramjet motors for missiles business,  was usually one-shot designs,  although I was able to get limited reuse out of some things for experimental purposes.  Our stuff was all ablative. 

For solid rockets,  we nearly always used a fiber-reinforced rubber as the case insulation,  to which the propellant was directly bonded (given the right primer) in the casting process.  These liners were laid up on expandable mandrels,  and pressure-cooked in place inside the motor case.  They were usually an EPDM-type rubber,  with initially asbestos fiber,  and later kevlar fiber. It started charring about 300 F,  and was fully charred through as it reached 600 F.  We just used a thickness such that it didn't char through until the burn was over.

In the ramjets,  the best choice was the far more erosion-resistant (by an order of magnitude) DC-93-104 loaded silicone rubber.  That's an ITAR material,  so I can't really tell you what's in it and how it works so well, but the Japanese offer a reasonable equivalent called Type 0 Shin Etsu.  I've used both of them.  This silicone system was necessary because the burn times were 10-100-or-more times longer.  You make it thick enough to just char through by end of burn,  or else you figure a way to retain the char,  which also made a decent insulator.  It charred at about 600 F or so.  Silicones really do survive at much higher temperatures than hydrocarbon polymers. 

Bear in mind that we had to control motor case temperatures when adjacent to flame in the 4000-6000 F range,  at anywhere from 100 to 3000 psi pressures.  If aeroheated on the outside,  we would have to add an insulator or coating outside,  too.  It was a really tough heat protection problem to solve.  But it was nearly always one-shot.  Reusable,  or steady state,  is much harder still.

This silicone stuff you pressure-cast around a hard mandrel in the case,  and then cook it to accelerate the catalyzed cure before extracting the mandrel.  You need an impermeable separator sheet bonded to it before you can cast propellant on it,  because the silicone in the liner is chemically incompatible with the hydrocarbon rubber in the propellant binder system.  The correct primers were required on both sides of the separator sheet,  which also had to have the right surface textures (because teflon sheet is otherwise a release agent). 

We usually used martensitic stainless steels for our motor cases,  like 4130,  or maybe D6ac.  It was more difficult and expensive to use alloy steels like 17-7PH,  but they do have better strength to higher elevated temperatures.  What we liked about 4130 was it was strong and sound and resistant to impact cracking even if soaked-out to -65 F cold,  while still fairly strong at substantially-elevated temperatures in the 1000-1200 F range.  Plus it was easier to work,  to get high strength by cold-working,  and to weld.

Some of the Sidewinder cases we made of aluminum,  because the customer specified it. Most were steel,  however. 

We did make third stage eject motor cases out of 6-4 alpha-phase titanium for Poseidon,  but these were literally carved out of big stock by machining away everything that didn't look like the case,  because that stuff is not formable.  Those were quite expensive. 

We did make experimentally some other motor cases out of a beta-phase formable titanium,  but these would age to useless weakness at room temperature in about 6 months.   Nothing useful there.

Believe me,  I understand about ceramic surface coatings.  There was a mag oxide /mag silicate slag produced copiously by one of the gas generator-fed ramjet fuels I played with.  That stuff would plate-out during the burn onto the charring surface of the silica phenolic liners in our heavyweight ramjet test hardware.  Having that hard slag ceramic coat atop the slightly-charred phenolic made the liners last for dozens and dozens of firings,  instead of just a single handful of tests.  The trick is less about which ceramic,  and more about how to actually install it to whatever you wish to protect.  In our case,  the slag was molten at near 2000 F,  while the phenolic was fully charred at 600 F.  It stuck to the char,  not the virgin phenolic,  which could only be char at the molten slag temperature.  But,  was it ever tough!

Not at the rocket plant,  but while working at a countermeasures house,  I had the opportunity to play with low density ceramics as a refractory,  non-ablative motor insulator.  My homemade stuff was similar to NASA's shuttle tiles,  except that the successful version of my stuff was a ceramic composite,  reinforced with ceramic fire curtain cloth.  It had about the density of the heavier grades of industrial styrofoam,  and a rather low thermal conductivity somewhere in the vicinity of 0.02 BTU/hr-ft-R.  Being reinforced,  it was structurally stronger than NASA's fragile tiles,  although it was still rather fragile itself.  I put several hours' burn at near 3500 F gas temperature on it,  including dozens of excursions of the combustor/inlet into violent rich blow-out instability.  A quarter-inch thickness of it held about a 12,000 F/inch thermal gradient for me.

That's my pedigree into heat protection and structural design,  obtained in the school of hard knocks.  I majored in aerothermo and propulsion,  and aerodynamics,  not really this stuff.

GW

Last edited by GW Johnson (2021-01-03 12:49:24)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#16 2021-01-03 17:22:38

louis
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Registered: 2008-03-24
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Re: Coast to Coast starship flights

I said there were challenges! And you've certainly mentioned a few.  However I think you can cross fuel cost off your list. If memory serves,  the cost for a "full tank" is something like $250,000. Correct me if I'm wrong, if I'm right that's abiut $800 per passenger of you have 300 passengers. We are probably talking about ticket prices in the $10,000 to $20,000 range for a flight from New York to Sydney or Shanghai.

Something you haven't mentioned is pasenger fitness. Probably only maybe 10% of normal airline passengers would be fit enough to undertaken the flights. They would need to complete a specialist training course that might take 2 or 3 days, I think this woukd become something of a status symbol for younger very wealthy people.

E2E is not going to supplant jet airliners. It is going to supplement them. It will be similar, to the 1930s when a small number of airships and intercontinental propeller planes drew traffic from the ocean-going liners .






kbd512 wrote:

Louis,

To be perfectly frank, electric airliners are much closer to engineering reality than a hypersonic rocket-powered VTOL airliner.  I'm only pointing out that the "huge challenges" faced are fuel burn rate, engine count, inert mass fraction (which determines vehicle durability), and passenger evacuation are intractable problems.  Rocket engines aren't going to become more fuel efficient unless they're no longer rocket engines, the engine count is what provides the necessary thrust to lift off to begin with, and the inert mass fraction is driven by the need for nearly all of the vehicle's weight to be propellant.  Since you're not going to reduce the fuel burn rate, use fewer engines than needed to get off the ground, nor change the fact that Starship would be an airliner sitting on its tail, I don't see how this will ever be practical.  It may be technologically feasible if every flight is perfectly executed, but no such success rate, relative to conventional airliners, has ever been demonstrated with rockets.  Individual jet aircraft have performed more power cycling associated with takeoffs and landings in a single day than any rocket engine has ever demonstrated in terms of total engine starts / stops.

Beyond that, all of those airport runways have already been paid for.  A Starship would require a large exclusion zone beyond the tiny pad footprint so that accidents don't throw shrapnel into homes a mile away, so the small size of the landing pad is another moot point.  When landing, there's no such thing as "line up and wait" with a rocket, either.  If one of these things ever crashes and throws debris onto the next closely-spaced landing pad, is the next inbound pilot supposed to land in a flaming wreckage pile?  No significant diversion is possible unless you're very high in the atmosphere.  These VTOL rockets come down like meteors.

If that wasn't enough, the window-destroying sonic booms would prevent it from ever diverting to alternate landing pads that aren't far away from population centers.  That was the entire point of Boom, and one of two reason it's fundamentally "different" from Concorde.  The other reason is a remarkable reduction in fuel burn, relative to lighting afterburners, which Concorde had to do to fly at Mach 2.  Boom changes "the sonic boom" into an acoustic wave form that doesn't trash windows or otherwise scare the crap out of people on the ground.  It sounds like a deep rumble, rather than the thunder that follows a lightning strike.  For various reasons, that's impractical for Starship.  Starship will never pass noise abatement ordinances on account of the fact that it's powered by six of the most powerful rocket engines on the planet.

Anyway, the military would probably have some kind of use for it, but they won't be going supersonic over CONUS with it, in the same way that existing regulation forbids them from breaking Mach unless there's some kind of inbound military threat.


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#17 2021-01-03 19:15:24

GW Johnson
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Re: Coast to Coast starship flights

Passenger fitness is not as big an issue to be feared as most folks suppose.  The big "threat" is pulling gees during ascent,  and maybe entry,  to and from LEO.   It really ain't much of a threat for operations to and from LEO. 

The gee exposure for any given burn during ascent ranges from just over 1 (no more than about 1.5) to around 3 or 4.  The exposure to gees in the 3-4 range is only several seconds long.  The entire ascent is only about 5 minutes long.  Usually,  there are two big burns (two stages). 

Reentry gee exposure ranges from under 1 to at most 3 or 4,  in a well-designed system.  The 3-4 gee exposure is only several seconds long.  The entire entry sequence is only about 3-4 minutes long.  You actually experience far higher gees as a shock load in the typical ocean splashdown,  but that is a pulse only milliseconds long. The short exposure time mitigates the hazard.

People endure higher gees riding roller coasters.  The peak exposure is shorter,  only a few seconds long.  The old wooden roller coaster with sequential loop-the-loops at 6 Flags Over Texas pulled 5 gees at the entry into the first loop,  and around 4 gees entering the second. 

Entirely untrained and physically-unfit people endured this just fine for many years,  and had fun doing it.  The bigger threat was actually rain.  At 55 mph out in the open,  rain in the face can really hurt.  That will NOT happen in spaceflight.  6 Flags recommended not riding if you had heart trouble,  but that was about the only consideration,  other than being tall enough to fit the restraint bar properly.

GW

Last edited by GW Johnson (2021-01-03 19:17:06)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#18 2021-02-15 10:46:41

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 21,860

Re: Coast to Coast starship flights

GW Johnson run down based on sn8 performance
http://exrocketman.blogspot.com/2020/12 … osion.html
it indicates not only the planned sea level engines plus vaccumn optimized as still requiring one moe engine for ssto

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