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#1 2014-10-17 17:16:55

SpaceGeek
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Registered: 2014-09-19
Posts: 6

Habcrafts and Cyclers

Robert Zubrin back in the 1990s proposed two possible means of transporting the vast number of immigrants required to colonize Mars. Of all the proposed methods, these two in my opinion are the most near-term and realistic. The first essentially uses a modified version of the Mars Direct Hab (with five decks instead of two) a Shuttle-Derived HLV and a NTR upper stage. The second uses SSTOs, chemical propulsion and a Cycler. The following quotes directly from his article "The Economic Viability of Mars" but all the information is also available in "The Case for Mars".

"If government sponsorship is available, the technological means required for immigration on a significant scale are essentially available today. In fig. 2 we see one version of such a concept that could be used to transport immigrants to Mars. An Shuttle derived heavy lift launch vehicle lifts 145 tonnes (A Saturn V had about this same capacity) to low Earth orbit, then a nuclear thermal rocket (NTR, such as was demonstrated in the USA in the 1960's) stage with an Isp of 900 s hurls a 70 tonne "habcraft" onto a 7 month trajectory to Mars. Arriving at Mars, the habcraft uses its biconic shell to aerobrake, and then parachutes and lands on its own sets of methane/oxygen engines.

The habcraft is 8 meters in diameter and includes four complete habitation decks, for a total living area of 200 m2, allowing it to adequately house 24 people in space and on Mars. Expansion area is available in the fifth (uppermost) deck after the cargo it contains is unloaded upon arrival. Thus in a single booster launch, 24 people, complete with their housing and tools, can be transported one way from Earth to Mars.

Now let us assume that starting in 2030 AD, an average of four such boosters are launched every year from Earth. If we then make various reasonable demographic assumptions, the population curve for Mars can be computed. The results are shown in fig. 3. Examining the graph, we see that with this level of effort (and the technology frozen at late 20th Century levels forever), the rate of human population growth of Mars in the 21st Century would be about 1/5th that experienced by colonial America in the 17th and 18th Centuries.

This in itself is a very significant result. What it means is that the distance to Mars and the transportation challenge that it implies is not a major obstacle to the initiation of a human civilization on the Red Planet. Rather the key questions become those of resource utilization, growing food, building housing, and manufacturing all sorts of useful goods on the surface of Mars. Moreover the projected population growth rate, 1/5th that of Colonial America, while a bit slow, is significant on a historical scale, and assuming a cost of $1 billion per launch, the $4 billion per year program cost could be sustained for some time by any major power on Earth that cared to plant the seeds of its posterity on Mars.

However, with a cost per launch of about $1 billion, the cost per immigrant would be $40 million. Such a price might be affordable to governments (for a time), but not to individuals or private groups. If Mars is ever to benefit from the dynamic energy of large numbers of immigrants motivated by personal choice to seek to make their mark in a new world, the transportation fee will have to drop a lot lower than this. Let us therefore examine an alternative model to see how low it is likely to drop.

Consider once again out CH4/O2 SSTO vehicles used to transport payloads from the surface of the Earth to low Earth orbit. For every kilogram of payload delivered to orbit, about 70 kilograms of propellant are required. CH4/O2 bipropellant costs about $0.20/kilogram, so $14 of propellant costs will be incurred for every kilogram lifted to orbit. If we then assume total system operation cost is 7 times propellant costs (roughly double the total cost/fuel cost ratio of airlines), then the cost of delivery to low Earth orbit (LEO) could be about $100/kilogram. If we assume that there is operating between Earth and Mars a cycling spacecraft which has the ability to recycle water and oxygen with 95% efficiency, then each passenger (100 kg with personal effects) will have to bring about 400 kg of supplies to provide himself with food, water and oxygen during a 200 day outbound trip to Mars. Thus 500 kg will need to be transported through a DV of about 4.3 km/s to move the immigrant from LEO to a (2 year period) cycling interplanetary spacecraft. The capsule mass, used to transport the immigrant from LEO to the cycler and from the cycler to the Martian surface could be assumed optimistically to have a mass of 500 kg per passenger. Thus for each passenger a total of 1000 kg needs to be delivered to the cycler orbit, which with an Isp of 380 s for the CH4/O2 propulsion system on the transfer capsules translates into 3200 kg in LEO. At a delivery price of $100/kg to LEO, and assuming that the cost of the cycler itself is amortized over a very large number of missions, this in turn translates into a cost of $320,000 per passenger to Mars.

Obviously, there are many assumptions in the above calculation that could be changed that would either raise or lower the calculated ticket price significantly. For example use of air-breathing supersonic ramjet propulsion to perform a significant part of the Earth to orbit DV could cut orbit delivery costs by as much as a factor of 3. Using an electric propulsion LEO to L1 electric propulsion ferry followed by a powered flyby through a LEO perigee using high thrust chemical stage would allow the cycler to be reached with a chemical DV of only 1.3 km/s, thereby doubling payload and reducing costs yet again. If the cycler employs a magnetic sail11 instead of simply using natural ballistic orbits with gravity assists, the hyperbolic velocity departing Earth required to rendezvous with it can be essentially zero, thereby allowing the entire LEO to cycler delivery to be done by electric propulsion, or conceivably even solar or magnetic sails. Increasing the degree of closure of the life support system on the cycler would reduce the consumable delivery requirement for each passenger, thereby reducing passage costs still more. Thus eventually Earth to Mars transportation costs could be expected to drop another order of magnitude, to $30,000 per passenger or so. The costs impacts as each of these innovations is progressively introduced is displayed in Table 3.

Table 3. Possible Cost Reductions of Earth to Mars Transportation System

                        Baseline  Advanced  Reduction Fare to Mars
                                              Factor
Baseline Mission          -------   -------     1.0   $320,000
Earth to Orbit            Rockets   Scramjets   0.3    $96,000
Life Support Closure        95%       99%       0.7    $67,000
LEO Escape Propulsion     CH4/O2      NEP       0.6    $40,000
Cycler Propulsion Natural Magsail               0.7    $28,000
"

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#2 2014-10-17 17:37:29

GW Johnson
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From: McGregor, Texas USA
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Re: Habcrafts and Cyclers

You can forget scramjets for launch purposes.  No airbreather has any frontal thrust density in the thin air above about 70,000 feet.  Scramjets do not reach speeds high enough to be useful until you are simply too high along your trajectory:  the air is too thin to produce the frontal thrust necessary to climb (THAT is why the X-30 "Orient Express" of about 1990 led nowhere).  You're better off with plain ramjet at lower altitudes.  The only real application I see for scramjet is lower-altitude / relatively short-range missile work. 

GW


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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#3 2014-10-17 18:58:17

SpaceGeek
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Re: Habcrafts and Cyclers

This is Zubrin's writting not mine. But what I think is significant is that even without all the technical improvements he suggested the basic Chemical Methane/Oxygen upper stage, Crew Capsule and Cycling spacecraft may be sufficient for mass immigration to Mars. Zubrin in his book "Entering Space" noted that immigrants coming to America in the 18th and 17th centuries spent seven or eight years salary just to afford the trip over. $320,000 would be equivelant to this in modern terms (the median household income in the US is $50,000) and the high wages from the massive labor shortage on Mars would probabley payback the cost quite quickly. The hardest part of the idea is the $100 per kg to LEO reusable SSTO.

I think Elon Musk's idea of $500,000 for a one-way ticket to Mars on the MTC is completely achievable eventually. In fact it's quite close to (if slightly more conservative)  Zubrin's estimates two decades earlier. The value of a Cycler is that you can reuse a billion dollar spacecraft countless times and artomorize the cost accordingly.

The other government sponsored model is also interesting however. According to the estimates made in the Case for Mars, Zubrin estimates that 100 years after such a program of immigration started the population on Mars would reach 80,000 (enough for terraforming?).

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#4 2014-10-17 21:28:23

SpaceNut
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Re: Habcrafts and Cyclers

"cost per immigrant would be $40 million" really not all that bad as I recall the Space Adventures brokered seven clients rides to the ISS starting with American businessman Dennis Tito for a reported $20 million payment, making him the first space tourist with Five Clients who participated in training only. Space Adventures is offering advance booking for a future lunar mission involving travel to circumnavigate the moon, on a circumlunar trajectory. Pricing has been announced at US$100 million per seat with no possible vehicle at this time from Russia to make use of....

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#5 2014-10-18 01:01:10

SpaceGeek
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Re: Habcrafts and Cyclers

SpaceNut wrote:

"cost per immigrant would be $40 million" really not all that bad as I recall the Space Adventures brokered seven clients rides to the ISS starting with American businessman Dennis Tito for a reported $20 million payment, making him the first space tourist with Five Clients who participated in training only. Space Adventures is offering advance booking for a future lunar mission involving travel to circumnavigate the moon, on a circumlunar trajectory. Pricing has been announced at US$100 million per seat with no possible vehicle at this time from Russia to make use of....

The problem is that $40 million/immigrant, while perfectly acceptable for government sponsored colonization (allowing an average of 100 people/year and a population growth comparable to 17th Century America), it limits the number of creative-driven individuals seeking to reach Mars to a relatively small number selected by a government agency. If Mars One has shown us anything, it's that thousands want to go to Mars now. In Zubrin's own words

"If Mars is ever to benefit from the dynamic energy of large numbers of immigrants motivated by personal choice to seek to make their mark in a new world, the transportation fee will have to drop a lot lower than this." Luckily if sufficiently low cost reusable SSTOs are developed ($100/kg to LEO) along with fully-reusable Cycling habitats, the privatelly-funded model (of individuals saving up and paying their own way) does become workable.

I doubt very many billionaires would spend $40 million for a one-way trip to Mars. Key words, one-way. The people going will be colonists, pioneers, rugged individuals on the frontier (ironically living quite communally), although I could imagine the odd Elon Musk type paying his way even in this scenerio.

The Habcraft honestly reminds me of the Conestoga Wagons from the old Frontier. They transported pioneers and the beginings of families across the frontier and then they were dissassembled upon arrival and used as building material for the first houses. The Habcraft works in a similar way in which 24 colonists fly out to Mars and upon arrival, use the Habcraft as their initial house for the first colonists. The inflatable greenhouse and tools are taken with them aswell. The upper (fifth deck) used for cargo on the way is used as additional living quarters after the cargo is removed upon arrival at the surface. Perhaps the first 6 children born on Mars will move into the uppermost deck before additional housing is built from InSitu materials (Plastic Domes, Brick Vaults etc). The entire proposal is extremely technically conservative colonizing Mars with only a Shuttle Derived HLVs, NTR upper stages, a large habitat module and use of InSitu resources (for oxygen, water, agriculture, manufacturing, transportation, mining etc).

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#6 2014-10-18 06:54:09

Tom Kalbfus
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Re: Habcrafts and Cyclers

The answer is robots, if we can replace a number of the launch crew with robots, we can reduce the launch costs.

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#7 2014-10-18 15:42:26

GW Johnson
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From: McGregor, Texas USA
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Re: Habcrafts and Cyclers

If you are setting up a real colony,  you are sending "mass quantities" of both people and supplies/equipment/materials to Mars.  You just don't do that with anything we have been launching these last 50+ years.  Those methods are too expensive,  and they always will be,  even if their price drops by a factor of 10. 

Robots vs humans will not get you that factor-10 price break;  plus,  a lot of us (myself included) don't trust machines.  I dislike flying on Airbus aircraft,  precisely because the pilot cannot override the computerized control system.  That already led to at least one fatal crash,  several years ago. 

A lot of the supplies and materials (especially liquid propellants) are capable of extreme acceleration.  These can be shot into orbit with light gas gun technology,  and recovered there by an orbital space tug.  It tows them to the orbit-to-orbit transport.  Other stuff,  like the people,  have to ride rockets or spaceplanes at low gee.  That'll be under $1000/lb soon,  maybe under $500/lb.  But not with government fiascoes like SLS.  With commercial things like Falcon-Heavy. 

The orbit-to-orbit transport is the key:  we can build landers for anything.  Conventional rocketry works for small exploration missions,  even setting up small bases.  But to plant a real colony?  That's a very large item (100's to 1000's of tons).  It gets too ridiculous too fast to ever be practical with the stuff we have been using. 

But there is something that works best/most efficiently in very large sizes (5000 tons and up),  and we have known exactly how to do it since 1959 (and I'm quite sure that 1955-vintage technology can be updated to make it even better).  It's called nuclear explosion propulsion.  Until there is "warp drive",  nuke explosion propulsion is your ONLY PRACTICAL method of planting LARGE colonies.  Anywhere.  Build a couple of these ships,  and use them for decades to centuries as orbit-to-orbit transports of immense size,  for setting up large colonies in a whole lot of places. 

GW


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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#8 2014-10-18 20:35:40

SpaceNut
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Re: Habcrafts and Cyclers

You are right SpaceGeek that only the Rich and elite have been to space and that an only one way ticket does pose a different set of variables that if he could if it was not for the money a common man would dare take the chance on as one would view that as a fresh start, one where the colonist would see it as a greener pasture over there at Mars.

I enjoyed the "Conestoga Wagons from the old Frontier analogy as to what the first colonist must do and that is recycle everything that can be repurposed for other uses.

Last edited by SpaceNut (2014-10-18 20:38:03)

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#9 2014-10-18 21:35:51

RobertDyck
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Re: Habcrafts and Cyclers

I still disagree with the idea of setting off a nuclear explosion with a spacecraft within the blast radius. Several problems: radiation, danger of blowing yourself up, and danger of dropping a nuke on Earth. And there's no way any country is going to allow putting nuclear bombs in space. Way to much danger of dropping one of those bombs on them.

There are many alternatives. Nuclear thermal rocket is one. Or the ultimate for in-space only: open cycle gas core nuclear thermal rocket. Fission fragments in exhaust mean that technology can only be used in space. However, radiation is much less than detonating a bomb.

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#10 2014-10-19 05:46:17

Antius
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Re: Habcrafts and Cyclers

I am a proponent of nuclear pulse propulsion.  But it probably isn't the only game in town as far as large scale, low cost launch is concerned.  The political issues that it would create essentially rule it out of any Western space programme in the foreseeable future.  Space colonisation would need to be the driving political ambition of the day before any government would sanction the construction of an Orion type launch vehicle.  You only need to remember the ridiculous international furore that surrounded the Fukushima accident to realise that an Orion programme would end up becoming the dominant international relations problem, on the same scale as the Iraq invasion of early 2000s.  Fukushima was a non-event in terms of its real radiological consequences, but the political and media reaction were enormous.  Can you imagine the public relations problem if a government deliberately released radioactive pollution on a similar scale?

The only way people might be persuaded to get behind an Orion programme is if you told them that the world was going to end and you needed to build spaceships big enough to evacuate the planet.  Under those circumstances, Orion is the only thing that would work and this is probably the only situation in which it could be made to work politically.

Since the original Case for Mars was written, it has pretty much become accepted wisdom that a reusable chemically fuelled SSTO is not workable as an economical rocket, for all the same reasons that the shuttle was unworkable economically.  The reusable vehicle is deadweight that eats into the payload budget and for an SSTO, the mass ratio is extremely slim to begin with.  There is questionable logic in burning fuel and spending money to put anything into orbit and then brining it down again.  Trying to engineer reusability into rocket engines and re-entry systems proved unworkable for the shuttle due to the enormous thermal stresses that these components must endure, and the engineers involved were not lacking in funding or technological expertise.  So we have an expensive, technologically complex launch vehicle that requires extensive refit between launches and all that cost ends up being spread over a tiny payload budget.  A reusable chemical SSTO would simply be another shuttle, probably an even more expensive shuttle than the last one.

Putting a nuclear engine in an SSTO would improve the payload budget, but would not solve the basic economic problems of the concept.  And you then have the difficulty and cost of developing, building and maintaining decay heat removal systems in a mass constrained vehicle, as well as shielding the crew in take-off and during EVA.  You would have the NRC or defence nuclear regulator on your back and since occasional launch failures are inevitable, you also have global political baggage to deal with.  All in all, I cannot see a nuclear SSTO being any cheaper or any more viable than a chemical SSTO.

So barring the development of a Polywell powered VASIMIR, space launch in the foreseeable future will depend upon non-reusable, chemically fuelled rockets.  The trick is to bring down the launch cost of those systems to affordable levels.  The best methods that I can foresee lay with the Big Dumb Booster concept.  Develop simple systems on a very large scale and generally use scale economies to bring down unit costs across the board.  That means ocean launch with big steel rockets, probably in the 500-1000te to LEO range.  Systems need to be simple and easy to fabricate using shipyard methods, with a single design developed as a national or even global standard and manufactured everywhere.  Maybe a large, two-stage, pressure-fed hybrid rocket system, using stabilised bitumous coal as the propellant or alternatively, a two stage NH3/O2 fuelled rocket, using jet pumps and simple ablative lined engines.  Use carbon steels with galvanised linings for the pressure vessels, engine and structure and a mixture of ablative linings and non-regenerative cooling in the engines.  Make the rockets big, technologically simple, and easy to build and then mass produce them on a huge scale.  In other words, the same philosophy that we apply to the manufacture of deodorant cans, which no one attempts to reuse.

Once in orbit, use reusable solar-powered VASIMIR cruisers to achieve trans-Mars injection or transfer to any other point in the solar system.  So the mission requirements of the BDB are always identical; launch from the equatorial ocean to a circularised 250km equatorial orbit.

The upper stage of the BDB could be broken down in orbital stations into propellant for the VASIMIR engines thus achieving reusability or sorts.  The lower stages can similarly be retrieved from the oceans and recycled, although not reused in the traditional sense.

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#11 2014-10-19 09:22:37

Terraformer
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Re: Habcrafts and Cyclers

The Case For Mars demonstrates Zubrin's singleminded zealousness for Mars, in that he completely neglects the possibility of getting propellent from anywhere other than Terra or Mars. A mature Lunar infrastructure, plus perhaps Martian farms, would mean passengers only have to bring themselves and their basic luggage. If we can bring launch costs per passenger (on a TSTO spaceplane system?) down to $100k (including, say, 20kg allowance of luggage), then the ticket cost to get to another world might be $200k, much less if they're only emigrating to Luna. Nowhere near as low as I want it, but then I want it to be available for everyone on Terra... smile Low enough that a large fraction of people could afford it by asset stripping themselves. As time goes on, the cost could approach $50-100k to move to Mars, affordable by the middle class.

Then, hopefully, we can get spaceflight as cheap as air travel today, and everyone can leave.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#12 2014-10-19 09:58:20

Void
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Re: Habcrafts and Cyclers

I might have missed it, perhaps it was already said, but a highly skilled person capable of productive behaviors hired for mineral extraction from asteroids and or Mars, must likely draw very large wages, and upon finishing that career might choose to settle on Mars, having a lot of wealth, being able to be a significant investor in business activity on that planet.

Mars would support the asteroid mining, Earth & Mars would get needed minerals.

As for another method, since there are so many people who might wish to go one way to Mars, perhaps a lottery.  Some of them would be willing to buy a ticket periodically, knowing that they were supporting the effort and had a small chance of winning a ticket.


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#13 2014-10-19 11:16:51

RobertDyck
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Re: Habcrafts and Cyclers

Antius wrote:

Since the original Case for Mars was written, it has pretty much become accepted wisdom that a reusable chemically fuelled SSTO is not workable as an economical rocket, for all the same reasons that the shuttle was unworkable economically.

It was also "accepted wisdom" that the world was flat.
It was "accepted wisdom" that no aircraft can fly faster than the speed of sound.
It was "accepted wisdom" that you cannot propulsively land on Earth, because fuel to do so would be prohibitively heavy. You require some sort of aerodynamic process to slow down, and approach the surface at a controlled rate. That could be a parachute, or wings, or lifting body. The chief engineer for Gemini tried to develop a "wing" that could be deployed like a parachute. He failed, so a conventional parachute was used. However, others continued his work and both the hang glider and parafoil were developed from that work. But the kicker is Dragon v2 does land propulsively.

Original requirements from NASA for the Space Shuttle were a fully reusable Two-Stage-To-Orbit vehicle. It would carry 11 metric tonnes to a space station in 400km orbit at 50° inclination. That's so close to the orbit ISS is in today that the difference isn't worth mentioning. This TSTO Shuttle would have a lifting body orbiter, and piloted fly-back booster. That means the booster would have an aircraft skin over insulation for the external tank, so no problem with foam. And no SRBs. Nixon demanded NASA and the military combine funds for a single launch vehicle, which created a Frankenstein's monster that wasn't good at anything. The Shuttle was changed to a delta wing so it could fly over the pole, but ironically it never did. The cargo hold was expanded to be large enough to carry the K7 spy satellite, and Shuttle was bulked up so it could lift 28.8 tonnes to 185km orbit. Shuttle requirements stated it would fly 50 missions per year, but after all the crap that was done to it, the maximum was 6 per year. Shuttle would have worked if it was built to original requirements.

Last edited by RobertDyck (2014-10-19 18:20:30)

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#14 2014-10-19 17:32:26

louis
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From: UK
Registered: 2008-03-24
Posts: 5,872

Re: Habcrafts and Cyclers

RobertDyck wrote:
Antius wrote:

Since the original Case for Mars was written, it has pretty much become accepted wisdom that a reusable chemically fuelled SSTO is not workable as an economical rocket, for all the same reasons that the shuttle was unworkable economically.

It was also "accepted wisdom" that the world was flat.
It was "accepted wisdom" that no aircraft can fly faster than the speed of sound.
It was "accepted wisdom" that you cannot propulsively land on Earth, because fuel to do so would be prohibitively heavy. You require some sort of aerodynamic process to slow down, and approach the surface at a controlled rate. That could be a parachute, or wings, or lifting body. The chief engineer for Gemini tried to develop a "wing" that could be deployed like a parachute. He failed, so a conventional parachute was used. However, others continued his work and both the hang glider and parafoil were developed from that work. But the kicker is Dragon v2 does land propulsively.

Original requirementss from NASA for the Space Shuttle were a fully reusable Two-Stage-To-Orbit vehicle. It would carry 11 metric tonnes to a space station in 400km orbit at 50° inclination. That's so close to the orbit ISS is in today that the difference isn't worth mentioning. This TSTO Shuttle would have a lifting body orbiter, and piloted fly-back booster. That means the booster would have an aircraft skin over insulation for the external tank, so no problem with foam. And no SRBs. Nixon demanded NASA and the military combine funds for a single launch vehicle, which created a Frankenstein's monster that wasn't good at anything. The Shuttle was changed to a delta wing so it could fly over the pole, but ironically it never did. The cargo hold was expanded to be large enough to carry the K7 spy satellite, and Shuttle was bulked up so it could lift 28.8 tonnes to 185km orbit. Shuttle requirements stated it would fly 50 missions per year, but after all the crap that was done to it, the maximum was 6 per year. Shuttle would have worked if it was built to original requirements.

I think this may be relevant to the discussion:

http://www.nasaspaceflight.com/2013/03/ … -missions/

Tie it into the Space X reusable rocket and perhaps you have a here a cheapish way of getting people to LEO orbit (from where they can be ferried to Mars) and bringing others back (from a Mars-Earth flight).


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

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#15 2014-10-19 18:32:20

RobertDyck
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From: Winnipeg, Canada
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Re: Habcrafts and Cyclers

louis wrote:

I think this may be relevant to the discussion:

http://www.nasaspaceflight.com/2013/03/ … -missions/

Tie it into the Space X reusable rocket and perhaps you have a here a cheapish way of getting people to LEO orbit (from where they can be ferried to Mars) and bringing others back (from a Mars-Earth flight).

Falcon 9R has a reusable first stage, with landing legs. And Dragon v2 is designed to land propulsively. The only things not reused are the "trunk" and upper stage. And SpaceX has plans to make the upper stage reused as well. No need to modify their plans, SpaceX is doing it all.

However, if you want a space plane, then put DreamChaser on Falcon 9R.

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#16 2014-10-19 20:20:44

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,729

Re: Habcrafts and Cyclers

If it were easy to build rockets everyone would be able to build one in there own back yard. Rather than dreaming of what we think we would need; lets start with what we know we will have using a stepping stone method to leverage it towards our desired destination, Mars.
Nasa's big dumb booster once built give the stremendous launch of mass to orbit while Falcon 9R gives the perfect taxi and supply train to build what we need in orbit to get us to mars on a one way mission with the follow up mission being a two way mission as by then another orbital assembly will be ready by then.

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#17 2014-10-19 21:09:57

RobertDyck
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From: Winnipeg, Canada
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Re: Habcrafts and Cyclers

GW Johnson wrote:

You can forget scramjets for launch purposes.  No airbreather has any frontal thrust density in the thin air above about 70,000 feet.  Scramjets do not reach speeds high enough to be useful until you are simply too high along your trajectory:  the air is too thin to produce the frontal thrust necessary to climb (THAT is why the X-30 "Orient Express" of about 1990 led nowhere).

Now what happens when you replace the SCRAM jet with a nuclear RAM jet similar to Project Pluto, but using Americium-242m to reduce nuclear material mass? "Tory" reactor for Project Pluto operated at 2,500°F. Add radiators with same glaze as black tiles from the Space Shuttle (HRSI) to reject heat into the high speed air stream. Even with compression heating of intake air, wouldn't that produce thrust at high altitude?

Interesting. The Eurofighter Typhoon uses EJ200 engines. Its turbine inlet temperature is 1,800°K. The temperture I just quoted for Project Pluto was 2,500°F which equals 1,644.26°K. So the engine for Typhoon already operates hotter than the reactor for Project Pluto.

And this news article from NASA says X-43A experienced high temperatures on its leading edges. When flying at mach 10, its hot spot was its nose at 3,600°F. That's 2,255.37°K. But what was the inlet temperature?

Last edited by RobertDyck (2014-10-19 22:26:19)

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#18 2014-10-20 06:13:24

Tom Kalbfus
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Registered: 2006-08-16
Posts: 4,401

Re: Habcrafts and Cyclers

As the technology more widely disseminates, what's to stop a third party from building a nuclear jet and flying it into space? Nuclear fuel does not get consumed as quickly as jet fuel, and all it has to do is heat the air and expel it out the back, and carry an additional supply or reaction mass to reach orbit. What is the United States going to do if Iran, China, or North Korea build a nuclear jet engine to launch satellites into space? The US already has sanctions on two of those, and if they slapped one on China, China has over one billion people, it might not need to trade with the outside world, the possibility is there than a future China might someday simply ignore environmental concerns and build a nuclear shuttle as a one stage vehicle to launch components of a space station into orbit. So what is the United States going to do then? Will in concede the space race, as China could lower its costs by using nuclear jet engines and rockets to get into space? China has already surpassed the US in GDP, if it wanted to, it could build nuclear launcher land men on the Moon and Mars and say "ha ha!"

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#19 2014-10-20 09:23:00

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,078
Website

Re: Habcrafts and Cyclers

1800 K is too high to be an inlet temperature for an aircraft under Mach 2.5 max speed. 

There are no alloys on the planet capable of withstanding the airloads and centrifugal stresses of turbine operation at more than about 2200 F (2660 R,  1478 K,  1205 C).  Whatever that temperature was,  it either wasn't K,  or it wasn't turbine inlet. 

Up to about Mach 6,  where the ideal gas assumptions are starting to break down significantly,  you can figure subsonic-duct inlet stagnation temperature rather easily from Mach number and OAT,  using an air specific heat ratio of 1.4 (decelerated like that,  inlet total is freestream total,  and inlet static is only a little bit less).  It goes up very fast and nonlinear with Mach number. 

I think the results are quite telling:  at 65,000 ft altitude/standard day conditions,  Mach 6 air total temperature is 2906 R (2446 F,  1614 K,  1341 C).  You can only heat the air in a combustor to about 4500-5000 R  (4040-4540 F,  2500-2778 K,  2227-2505 C) before too much ionization sets in to derive any thrust out of the nozzle at all.  Without max heating,  frontal thrust density falls,  even as frontal drag density is going up as the square of Mach number.  (ASALM-PTV reached Mach 6 on the one flight test,  barely,  at lower altitude.) 

1800 K for the Eurofighter sounds more like an afterburner temperature to me.

Scramjet is a way to sidestep this problem by never decelerating the air subsonic inside the engine.  Unfortunately,  you incur a whole host of problems doing this that have been very intractable for over 60 years.  You can count the number of successful test flights of scramjet engines on the fingers of 2 hands,  worldwide.  It is not a technology in any way ready to apply. 

The old Project Pluto engine was a subsonic "combustion" ramjet heated by a nuclear reactor instead of combustion.  Its core mountings were operating about 10-20 degrees F (R) below their meltpoints at flight power.  Hardware life was never very long in test,  and test it they did,  on the ground in Nevada,  not far at all from the Jackass Flats nuke rocket facility.  This thing was a low-altitude strategic cruise missile at Mach 3,  under 5000 ft altitude.  Its radiation trail,  and the trailing shock wave,  would have killed more people than the 5 megaton warhead it was to carry.  No,  nobody is going to fly a technology like that. 

The problem with high altitude airbreather thrust density isn't the heat,  it's the low ambient air density.  You inlet is scooping up a large volume that just has no appreciable mass.  Thrust is massflow.  Low massflow,  low thrust.  Simple as that. 

GW


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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#20 2014-10-20 10:07:18

Tom Kalbfus
Banned
Registered: 2006-08-16
Posts: 4,401

Re: Habcrafts and Cyclers

Well if it kills, then it is a weapon, so might not the Chinese use such a thing, the Chinese did after all kill 50 million of their own people in the Cultural Revolution, and they show little concern for pollution when they burn coal in their power plants. If the Chinese want to build a base on Mars, they might very well be willing to sacrifice human lives to do it. So what would the United States do if the Chinese chose to conquer space in this manner?

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#21 2014-10-20 12:37:02

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 6,172
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Re: Habcrafts and Cyclers

The Wikipedia article for EJ200 engines states the turbine inlet temperature was 1,800°C. Not the compressor inlet temperature. Would that be after the combustion chamber, before the turbine? Also, doesn't the EJ200 use ceramics to withstand extreme heat?

Wikipedia for Typhoon states:
Service ceiling: 16,765 m (55,003 ft (up to 64,000–70,000 ft))
Absolute ceiling: 19,812 m (65,000 ft)

I assume that means absolute ceiling can only be achieved with no weapons and minimal fuel load. And expect poor acceleration, and only a narrow speed range.

On the other hand, Wikipedia for SR-71A Blackbird states:
Maximum speed: Mach 3.3 (2,200+ mph, 3,540+ km/h, 1,910+ knots) at 80,000 ft (24,000 m)
Service ceiling: 85,000 ft (25,900 m)

However, I remember in the 1970s a news article about a world speed record. Some British aircraft manufacturer claimed to have the fastest aircraft in the world. So the SR-71 guys brought one of their planes to the same test range in the UK, and flew the same test run. Two runs over the same ground, one in each direction so wind wouldn't be a factor. They timed how long it took to fly from one ground marker to another. They announced that they flew faster than the British plane, so the Blackbird was still the fastest aircraft in the world. But they refused to publish exactly how fast. But they failed to account for British tabloid reporters. Some reporters watched with binoculars and a stop watch. They timed the Blackbird, and calculated a speed of mach 3.6. That was the fastest at the time, so the Blackbird did continue to hold the world record. But that speed was published in all British Commonwealth countries. Americans responsible for the Blackbird were pissed off! They didn't want the exact number published. One lesson: don't fly your secret plane over ground you don't control.

But someone on this forum (was it you Mr. Johnson?) stated the Blackbird's engine would start to melt at mach 3.8, so mach 3.6 was the practical limit anway.

If an aircraft designed in the 1960s can fly that fast at 80,000 feet, they why can't a modern aircraft fly faster? If the limit is 80,000 or 85,000 feet, then fine. If we can get up to mach 17 at 85,000 feet or whatever, then turn up for the final push to space, then good enough. And I pick that speed because SCRAM jet guys at one point claimed they seriously hoped to achieve that.

Last edited by RobertDyck (2014-10-20 17:02:48)

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#22 2014-10-20 12:49:00

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Habcrafts and Cyclers

RobertDyck wrote:
louis wrote:

I think this may be relevant to the discussion:

http://www.nasaspaceflight.com/2013/03/ … -missions/

Tie it into the Space X reusable rocket and perhaps you have a here a cheapish way of getting people to LEO orbit (from where they can be ferried to Mars) and bringing others back (from a Mars-Earth flight).

Falcon 9R has a reusable first stage, with landing legs. And Dragon v2 is designed to land propulsively. The only things not reused are the "trunk" and upper stage. And SpaceX has plans to make the upper stage reused as well. No need to modify their plans, SpaceX is doing it all.

However, if you want a space plane, then put DreamChaser on Falcon 9R.

Interesting, though little mention of costs I note.  The X-37B appears to be launched using a Delta-2.  That being the case, what does the reusable part of the vehicle actually do, aside from eat into the payload budget?

If I recall correctly, both the shuttle main engines and heat shield required refurbishment after each launch and the engines complete replacement after just 3 launches.  The shuttle had a payload capability of ~24 tonnes to a 400km orbit.  Compare this to the expendable Shuttle C variant, which could deliver 70 tonnes to the same orbit.  The Shuttle C included the shuttle main engines and external tank, but replaced the reusable vehicle with a hollow payload container.  The engines would have been discarded after a single use, but the payload to orbit per launch would have almost tripled and the maintainance costs of that complex reusable vehicle would have disappeared.

Maybe the original concept would have allowed better reusability and superior economics.  But it clearly would have had a long way to go to get down to even Delta-2 launch costs, let alone compete with Russian launch vehicles on an equal cost basis.

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#23 2014-10-20 13:05:08

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Habcrafts and Cyclers

RobertDyck wrote:

The Wikipedia article for EJ200 engines states the turbine inlet temperature was 1,800°C. Not the compressor inlet temperature. Would that be after the combustion chamber, before the turbine? Also, doesn't the EJ200 use ceramics to withstand extreme heat?

Wikipedia for Typhoon states:
Service ceiling: 16,765 m (55,003 ft (up to 64,000–70,000 ft))
Absolute ceiling: 19,812 m (65,000 ft)

I assume that means absolute ceiling can only be achieved with no weapons and minimal fuel load. And expect poor acceleration, and only a narrow speed range.

On the other hand, Wikipedia for SR-71A Blackbird states:
Maximum speed: Mach 3.3 (2,200+ mph, 3,540+ km/h, 1,910+ knots) at 80,000 ft (24,000 m)
Service ceiling: 85,000 ft (25,900 m)

However, I remember a news in the 1970s article about a world speed record. Some British aircraft manufacturer claimed to have the fastest aircraft in the world. So the SR-71 guys brought one of their planes to the same test range in the UK, and flew the same test run. Two runs over the same ground, one in each direction so wind wouldn't be a factor. The timed how long it took to fly from one ground marker to another. They announced that they flew faster than the British plane, so the Blackbird was still the fasted aircraft in the world. But they refused to publish exactly how fast. But they failed to account for British tabloid reporters. Some reporters watched with binoculars and a stop watch. They timed the Blackbird, and calculated a speed of mach 3.6. That was the fastest at the time, so the Blackbird did continue to hold the world record. But htat speed was published in all British Commonwealth countries. Americans responsible for the Blackbird were pissed off! They didn't want the exact number published. One lesson: don't fly your secret plane over ground you don't control.

But someone on this forum (was it you Mr. Johnson?) stated the Blackbird's engine would start to melt at mach 3.8, so mach 3.6 was the practical limit anway.

If an aircraft designed in the 1960s can fly that fast at 80,000 feet, they why can't a modern aircraft fly faster? If the limit is 80,000 or 85,000 feet, then fine. If we can get up to mach 17 at 85,000 feet or whatever, then turn up for the final push to space, then good enough. And I pick that speed because SCRAM jet guys at one point claimed they seriously hoped to achieve that.

Looking in my heat transfer textbook I note that only a handful of materials have melting points greater than 2000C.  Aluminium oxide (2050C), berylium oxide (2450C), boron (2300C), Pyrolytic graphite (2000C), silicon carbide (2820C), thorium dioxide (3300C).  Of course we could bleed a high heat capacity cooling through pores in the surface to cool it (ammonia?).  That way the surface remains much cooler than the airstream.  I also note that thermal conductivity of these materials drops rapidly with increasing temperature and there is no information on how strength declines with temperature.  So it would be wise to keep the surface beneath 1000K.  If the acceleration phase is short (100s?), then the required mass of bled cooling could be modest, especially when you account for evaporation and dissociation of the ammonia.

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#24 2014-10-20 13:09:50

Terraformer
Member
From: Lancashire
Registered: 2007-08-27
Posts: 3,304
Website

Re: Habcrafts and Cyclers

I wonder how much the original shuttle plan would cost to develop today... mind, 11 tonnes to orbit is a lot for a reusable spacecraft. I presume they planned on launching vertically?

At the moment, I'm leaning towards something similar to the Lynx spacecraft, except with jet engines to allow flyback and bigger tanks to allow it to go much faster, then launching an expendable upper stage. Much like Black Colt, really. I think that by itself would be able to cut the cost of putting small payloads into orbit by a very significant amount. Once that's been flying for a while, perhaps redesign it with a ramjet, so it can go faster, even launch a small manned spaceplane upper stage? Maybe we can push it further from there with a scramjet, and get ourselves a hybrid rocket SSTO... but I don't want to start with that goal.

It might not even cost $100 million to develop... http://forbesindia.com/article/cross-bo … et/38224/1. Hey, the biggest crowdfunding to date has raised over $50 million...


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#25 2014-10-20 13:16:39

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 6,172
Website

Re: Habcrafts and Cyclers

Shuttle when it first launched could lift 24 metric tonnes to 185km orbit. It was upgraded a few times, the last before construction of ISS. After all upgrades, it could lift 28.8 tonnes to 185km orbit, or 16.050 tonnes to ISS.

Frequency of engine swap-out was controversial. I also read engines had to be swapped for overhaul after 3 launches, but saw an interview with an astronaut who claimed the number of launches was greater. She didn't say how many, just that it was a defined schedule. Some service after 3 launches, complete swap-out after a larger number. I wish she said exactly what the schedule was. She was an engineer so should have known these things.

One great expense of the Shuttle was overhead. They took the annual cost of NASA centers to support the Shuttle, and pro-rated over the number of launches per year. So fewer launches, more cost per launch. The centers were designed for a rate of 50 launches per year; at only 6 it was ridiculous.

This is one concern I had with DreamChaser. The orbiter doesn't include main engines, so there's very little return for the mass launched. But the spacecraft is reused, which is a major expense. However, once Dragon v2 starts to fly, carrying crew and reusable, that raises the question whether the mass of a lifting body is worth it. Reusability is the primary advantage of a mini-Shuttle. But if a capsule can be reused, and much lower mass? Umm...

Then again, Boeing's Orion/MPCV/CST-100 is not designed to be reused at all.

Last edited by RobertDyck (2014-10-20 17:26:04)

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