Why Space X is the best...

GW Johnson · 2017-11-19 20:36:19

Kbd512:

I didn't say anything at all about whether the Spacex ITS is the right way to start a settlement on Mars. All I said was that entry flight path they have come up with was an impressive piece of design. 97% of the entry velocity gets killed by drag, leaving only about a quarter of a km/s to kill with retropropulsion. Very impressive indeed.

In point of fact, what they came up with is a variation on the pull-up and tailslide idea from 1950's science fiction, specifically "Rocky Jones, Space Ranger" from 1956.

Also in point of fact, I think something much smaller would be more appropriate to scope-out suitable sites, including a small dozer or loader to clear off a flat landing field. Then landing something with a high length/leg span ratio around 4 or 5 makes sense from a reliability standpoint. But for landing on rough, unprepared ground, that length to leg span ratio should never, ever, ever exceed 1.

There's multiple possible mission architectures that would actually wok. I agree with you about sending things ahead unmanned, with electric propulsion. I disagree about the "tin can hab" idea, because those are invariably too small for a crew to stay sane for long confinement. 100 cubic meters volume per person is a bare minimum, and then only if it is arranged correctly, and reconfigurable by the crew. This extends not just to the transit spacecraft, but also to the on-the-ground habitations.

My own idea for the initial missions was to use a chemically-propelled orbit-to-orbit transport to bring the crew to Mars orbit, and to return them all the way to Earth orbit, so the transport could be refurbished, refilled, and reused for other missions. Its return propellants would be sent ahead unmanned using electric propulsion.

The landers were one-stage reusable (and thus inherently-large), sent ahead along with their propellant supplies to Mars orbit, unmanned, by electric propulsion. These large vehicle are quite suitable as habitat spaces for short stays (a couple of weeks to a month) at each site to be explored. Sending 3 such allows you to alternate crews to the surface, and still have landers to support surface rescues, even if one fails. When you do that, then having an abort-to-surface escape capsule as the tip of the lander makes real sense. Such landers are essentially conical with a neck, and a heat shield across the base. That shape resembles a Mercury or Gemini capsule, just scaled way up.

Basically, until you identify the site you really want, you never have to precision-land multiple vehicles on one site at all. That gives the alternate crew in orbit time to establish the equivalent of some GPS satellites to support that final precision landing, including clearing a flat landing field for Musk's big, tall ship. Once you have a safe place for it to land, then Musk's giant-ship idea makes real sense. It's the equivalent to the LST's we used at D-Day, and at Inchon.

GW

Last edited by GW Johnson (2017-11-19 20:43:00)

SpaceNut · 2017-11-19 21:06:31

Going to minimalist may also be the wrong direction as we want to show that we can do more than land and come back after a short time.

louis · 2017-11-20 04:10:41

I am amused at how those sci-fi representations of rockets landing on Mars from the 50s - which once looked so clunky during the era of f Apollo and the Space Shuttle - now appear pretty realistic!

GW Johnson wrote:

Kbd512:
In point of fact, what they came up with is a variation on the pull-up and tailslide idea from 1950's science fiction, specifically "Rocky Jones, Space Ranger" from 1956.

GW

louis · 2017-11-20 04:16:00

Yep, I think we are "beyond minimalism" now. I once argued for super-minimalist missions, but now I think with the Space X game plan we are in a very different era. Essentially Mission One will offload the equivalent of 10 houses in terms of mass. It's like taking a little hamlet all the way from Earth to Mars in one go. The potential to "do stuff" is immense.

I think exporting an industrial infrastructure in miniature should be the main focus of Mission One. Clearly this will be done with respect to propellant production, but I hope Space X go further and export a lot of industrial start up equipment on Mission One. I don't feel agriculture is a prime objective for Mission One - maybe a side project. Feeding a few people will not be a problem. A full scale agriculture project could probably wait a few years. However, since Musk started the whole thing with the aim of getting an automated greenhouse to Mars I am sure plant production will feature somewhere!

SpaceNut wrote:

Going to minimalist may also be the wrong direction as we want to show that we can do more than land and come back after a short time.

RobertDyck · 2017-11-20 05:05:44

GW Johnson wrote:

In point of fact, what they came up with is a variation on the pull-up and tailslide idea from 1950's science fiction, specifically "Rocky Jones, Space Ranger" from 1956.

I tried to find a clip. I found full episodes on YouTube, dated 1954. Here's a clip showing a landing, with full Hollywood dramatization. The link starts at the landing.

louis wrote:

I am amused at how those sci-fi representations of rockets landing on Mars from the 50s - which once looked so clunky during the era of f Apollo and the Space Shuttle - now appear pretty realistic!

It's a matter of believing you can do it. When you believe you can, you put in the time and effort to make it happen. When you believe you can't, you find excuses to not do the work. They started with Dyna-Soar, an aircraft launched on a rocket. They had built aircraft and knew how to land one, and built rockets for missiles, so believed they could do it. Then Russia launched Gagarin, so they had to do as well and do it quickly. They studied hypersonic aerodynamics and found a blunt body worked best when re-entering. The Mercury shape was a blunt heat shield with the rest of the capsule following the air stream behind the heat shield. Fighter jets already used an ejection seat, so they needed to get the astronaut back into the atmosphere where a parachute could work. Dropping a capsule on land would hit hard, so they splashed in water. And chose the ocean because their aim wasn't good.

The next step was a reusable spacecraft. They did a lot of work on a lifting body, so it could land like an aircraft. However, that was cancelled for reasons we've gone over many times. They had already done a lot of work on X-20 Dyna-Soar, so they went back to the Dyna-Soar idea but made big. That was Shuttle.

One Senator sponsored a program to have the Air Force build DC-X to show NASA how it's done. It was done quickly, inexpensively, and effectively. They did something NASA thought couldn't be done: land a rocket on its tail. Falcon 9 is based on that.

The next question is whether it's best. A lifting body like Dream Chaser can land on a runway; no need for a ship to go fish it out of the ocean. It's a lot more practical. X-38 tried to do the same, but was based on the lifting body shape of X-24A which had a control problem at low speed. You don't want a control problem when landing. X-38 solved that with the largest parafoil ever built at that time. And it lands on skids. X-38 could be retrieved by a flat bed truck with a truck crane, and perhaps a minivan for crew. That's a lot more practical than an aircraft carrier battle group like Apollo. However, Dream Chaser uses the HL-20 lifting body shape, which can land on a runway. It's easier if the craft lands itself at the launch site, and crew can just walk off. The problem with Shuttle and Dyna-Soar is they used expendable boosters. Shuttle partially resolved that by putting main engines on the orbiter, only an external tank was expended, but SRBs cost too much to recover and reuse, 90% the cost of new ones. The original TSTO Shuttle design from 1968 would land both on a runway. VentureStar was SSTO, lifting body that would land on a runway. The problem with VentureStar wasn't technical, it was management. Lockheed-Martin wanted to charge NASA for a cost over-run when their last minute change of the tank didn't work. It was changed from solid wall composite to hollow wall honeycomb structure. NASA wouldn't pay for the cost over-run, Lockheed-Martin refused to share the cost, so halted all work. There was a proposal to go back to aluminum alloy, but that added so much weight that it made the vehicle not feasible. All the figures still look like it would have worked with the original solid wall composite tank.

Of course if you want a truly reusable launch vehicle, it'll required advanced propulsion.

Last edited by RobertDyck (2017-11-20 13:06:40)

louis · 2017-11-20 06:33:54

I didn't know Falcon 9 had a precursor in that way. Are you sure DC-X didn't nick the UK's Harrier jumpjet technology?

RobertDyck wrote:

One Senator sponsored a program to have the Air Force build DC-X to show NASA how it's done. It was done quickly, inexpensively, and effectively. They did something NASA thought couldn't be done: land a rocket on its tail. Falcon 9 is based on that.

RobertDyck · 2017-11-20 13:31:06

louis wrote:

I didn't know Falcon 9 had a precursor in that way. Are you sure DC-X didn't nick the UK's Harrier jumpjet technology?

Actually the US attempted to develop VTOL aircraft before Harrier; they just failed. Aircraft the US developed mostly landed on their tail like a rocket. This made it extremely difficult to fly. One aircraft was test landed on a carrier ship. One expert test pilot was able to do it, but no other pilot was able to land the thing. The aircraft is useless if nobody can fly it.

Convair XFY Pogo

Lockheed XFV Salmon

Ryan X-13 Vertijet

SNECMA Coléoptère (This was a French design from the 1950s. Others were American.)

louis · 2017-11-21 05:32:17

Thanks for those pics and the quick tutorial Robert - v interesting.

RobertDyck wrote:

louis wrote:
I didn't know Falcon 9 had a precursor in that way. Are you sure DC-X didn't nick the UK's Harrier jumpjet technology?
Actually the US attempted to develop VTOL aircraft before Harrier; they just failed. Aircraft the US developed mostly landed on their tail like a rocket. This made it extremely difficult to fly. One aircraft was test landed on a carrier ship. One expert test pilot was able to do it, but no other pilot was able to land the thing. The aircraft is useless if nobody can fly it.
Convair XFY Pogo
https://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Convair_XYF-1_Pogo.jpg/170px-Convair_XYF-1_Pogo.jpg
Lockheed XFV Salmon
https://upload.wikimedia.org/wikipedia/commons/thumb/3/31/Lockheed_XFV-1_on_ground_bw.jpg/300px-Lockheed_XFV-1_on_ground_bw.jpg
Ryan X-13 Vertijet
https://upload.wikimedia.org/wikipedia/commons/thumb/a/ac/Ryan_X-13.jpg/300px-Ryan_X-13.jpg
SNECMA Coléoptère (This was a French design from the 1950s. Others were American.)
https://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/SNECMA_Col%C3%A9opt%C3%A8re_on_ramp_1959.jpg/300px-SNECMA_Col%C3%A9opt%C3%A8re_on_ramp_1959.jpg

kbd512 · 2017-11-21 11:39:07

If RamGen’s (Dresser-Rand’s now, I guess) supersonic CO2 compressors were developed further, how much rocket fuel would be required to operate that sort of “jet” engine for a few minutes if it turns out that the landing area is not as compacted as was previously thought?

A pure rocket propulsion system leaves few options for the crew if the landing area isn't what was expected. The supersonic compressors are considerably lighter and smaller than their subsonic counterparts, which wouldn't work in the thin Martian atmosphere anyway, so I would think that an equivalent quantity of rocket fuel would provide at least a couple minutes of "hover" so that the crew could re-position the ship in a short "hop" just to get a stable spot to set down. I'm under no illusion that it would be lighter than rocket engines, but if they're absolutely intent on a tail first landing, why not add the ability to however for a couple minutes or so?

If that's too complicated or heavy, then what about folding landing gear feet that widen the landing gear base a bit? If even that's too complicated or there isn't enough space, then what about guns that drive stakes into the regolith when the lander touches down? Electromagnetic locking blocks could "release" the stakes so the ship can take off again when it's time to return to Earth. Firing could be coordinated with pressure sensors that determine how "hard" the ground is and electronics can ensure that it happens after all legs have touched the surface and automatically shut down the rocket engines upon firing.

Of all the potential ways to anchor the ship to the ground, I would think that explosively driven anchoring stakes have to be the lightest and require the fewest modifications and development but I could be wrong.

Anyway, just some thoughts for others to pick apart.

louis · 2017-11-30 19:17:43

Space X had no problem in raising $450 million in a few months...

https://www.geekwire.com/2017/spacex-100-million/

I think that supports my analysis that commercialisation is going to generate huge amounts of revenue and investors can see that.

SpaceNut · 2017-12-02 20:57:39

Well that is why he can send up a Tesla Roadster with David Bowie on the stereo in the brand new rocket, known as the Falcon Heavy.

Falcon Heavy to launch next month from Apollo 11 pad at the Cape.

Musk's announcement of the planned launch of the giant rocket comes just over two months after he outlined his vision for eventually putting humans on Mars and colonizing the planet.
That project will require an even larger rocket, though. It's called the BFR, or Big Falcon Rocket, which inside the company is nicknamed the "Big F--king Rocket."
SpaceX plans to start building the first of those by the middle of next year, Musk said in late September.
He wants to land at least two of the spacecraft on Mars in 2022 carrying equipment -- and then ones transporting people in 2024.
In the meantime, the Falcon Heavy is intended to boost the amount of cargo SpaceX can take into space for its customers. The company says it will be able to take into orbit more than twice the payload -- 119,000 pounds -- of its closest rival at a third of the cost.

SpaceNut · 2017-12-11 21:45:13

SpaceX readies used rocket for space station flight for launch Tuesday on a flight to deliver 4,800 pounds of equipment and supplies to the International Space Station. It will be the California rocket builder's 17th flight so far this year.

The launching will mark the fourth time SpaceX has reflown a recovered Falcon 9 first stage -- a first for NASA -- and the second time the California rocket builder has re-launched a Dragon supply ship.
Assuming an on-time launch, the Dragon will reach the space station early Friday, pulling up to within about 30 feet and standing by while astronauts operating the station's robot arm lock onto a grapple fixture. From there, the cargo ship will be pulled in for berthing at the Earth-facing port of the station's forward Harmony module.
Packed in the capsule's pressurized compartment: nearly 1,000 pounds of crew supplies, nearly 2,900 pounds of science material, spacewalk equipment, space station hardware and computer components. Among the experiments is one sponsored by beer-giant Budweiser to learn more about how microgravity affects barley seeds.
Mounted in an unpressurized "trunk" section are two external science packages, one to measure how much solar radiation Earth receives and another to help characterize the space debris environment.

Oldfart1939 · 2017-12-15 10:08:28

Well guys, I just watched the latest SpaceX launch and first stage recovery, wherein the Dragon spacecraft was a previously flown one, and the first stage booster was also a "flight-proven" stage. SpaceX is calmly demonstrating that their "outside the box" thinking and engineering are far superior to that of the NASA planners and that of the OldSpace contractors.

https://youtu.be/-70JIavHyHE

louis · 2017-12-15 17:32:58

Absolutely Oldfart! You nailed it!!!

Oldfart1939 wrote:

Well guys, I just watched the latest SpaceX launch and first stage recovery, wherein the Dragon spacecraft was a previously flown one, and the first stage booster was also a "flight-proven" stage. SpaceX is calmly demonstrating that their "outside the box" thinking and engineering are far superior to that of the NASA planners and that of the OldSpace contractors.
https://youtu.be/-70JIavHyHE

louis · 2017-12-16 20:05:42

https://www.youtube.com/watch?v=r4XJS_oftH8

I never tire of these first stage rocket landings! Brilliant execution. Space X must be up to a 90% success rate by now.

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