Are spacecraft looking more futuristic?

[Mike!]

If your end goal s space tourism, you darn well better make the transport as cool looking as possible.

 

[Beelzebuddy]

If your end goal s space tourism, you darn well better make the transport as cool looking as possible.

For space tourism, the view out the window matters much more than what the window frame looks like. But when the view out the window is purely imaginary, as it is today, the window frame is all we have to go on. Their end goal may be space tourism but their immediate goal is reassuring investors that they'll eventually get there, and devoting effort to making demonstrations sexy is an ironically counterproductive way of doing that.

 

[barehl]

I see that several people seem to have the wrong idea about Dragon V2. It isn't like SpaceshipOne which was a prototype that only needed to fly enough to win the prize. The Dragon resupply craft has already made five missions so we know the craft itself works just fine. If there are shortcomings with seats, these should be made clear when crash dummies are used.

At any rate, the problems will be worked out. SpaceX has no choice since Boeing is only about 6 months behind with their own CST-100. And, Boeing was smart enough to design it so that it would fit on SpaceX's own Falcon 9 rocket. So, either SpaceX will get the Dragon V2 up to proper condition or they will be flying Boeing's craft. I have no doubt that Boeing can handle the design, but again, Dragon is already flying. Particularly with Putin's behavior, there is a lot of pressure to stop relying on Russian crew transport. One or both of these craft will be the main human transport for NASA.

 

[barehl]

I'll put this here since this thread already covers the Dragon V2 vehicle. After the long, dry spell at NASA following the decommissioning of the Shuttles in 2011, this video to me is very impressive, quite reminiscent of early Apollo. Again, this is a new, human-carrying craft, the first in the US since the Shuttles.

Dragon V2 Pad Abort Test


Well, actually I guess NASA's Orion would be the first. However, it hasn't done anything since the flight test last December whereas Dragon's test program will continue until it routinely carries people. There is no plan that I am aware of for Orion to carry people for several years. The race now is whether Dragon or CST-100 will carry people first.

 

[Corsair 115]

Futuristic spacecraft? Can we have one of these yet? This one's pretty spiffy too!

 

[Damien Evans]

I'll put this here since this thread already covers the Dragon V2 vehicle. After the long, dry spell at NASA following the decommissioning of the Shuttles in 2011, this video to me is very impressive, quite reminiscent of early Apollo. Again, this is a new, human-carrying craft, the first in the US since the Shuttles.

Dragon V2 Pad Abort Test


Well, actually I guess NASA's Orion would be the first. However, it hasn't done anything since the flight test last December whereas Dragon's test program will continue until it routinely carries people. There is no plan that I am aware of for Orion to carry people for several years. The race now is whether Dragon or CST-100 will carry people first.

That's not entirely true. Just because it hasn't been launched since doesn't mean work on it has stopped.

 

[BazBear]

Futuristic spacecraft? Can we have one of these yet? This one's pretty spiffy too!

I had a funny feeling before I clicked those links that you were going to go Space: 1999 on us. Not that I blame you

 

[Corsair 115]

I had a funny feeling before I clicked those links that you were going to go Space: 1999 on us. Not that I blame you

We're sixteen years past due on those spacecraft, darn it!

 

[barehl]

That's not entirely true. Just because it hasn't been launched since doesn't mean work on it has stopped.

No, the work hasn't stopped; they are working on SLS at Michoud right now. For Orion they are mostly doing review because the December flight test was with a prototype version called EFT-1. This is being redesigned to be lighter and easier to build for EM-1.

The video I posted was the pad abort test of the escape system on Dragon V2. The same test for Orion was May 6, 2010. The flight abort test for Orion has been pushed back to after the EM-1 test which is currently scheduled for September, 2018. EM-1 is an unmanned flight out to the moon and back. This will also be the first flight test of SLS. The project director, Geyer, says that it is due to budget constraints. The first crewed flight would be EM-2 which isn't scheduled until 2021.

Let's look at both timelines:

2004: Delta IV Heavy first flight, partial success
2005: Request for proposals for Orion.
2006: Griffin sets Orion design as CEV based on Apollo hardware with the ambitious goal of carrying crew by 2012.
2007: Delta IV Heavy second flight successful
2008:
2009: Ares 1-X first flight test. Augustine Committee reports Constellation behind schedule, over budget, still 8-10 years from carrying crew.
2010: Orion pad abort test. Constellation canceled, replaced with SLS.
2011: Orion CEV design changed to MPCV
2012:
2013:
2014: Orion flight test EFT-1 on Delta IV Heavy
2015: Ground testing of SLS engines. Ground testing SLS solid rocket engines.
2016:
2017:
2018: Orion EM-1 SLS test flight. Orion flight abort test, Peacekeeper booster.
2019:
2020:
2021: Orion EM-2 crew flight


2005: Request for proposals for ISS resupply
2006: SpaceX awarded COTS contract for Falcon 9
2007:
2008: SpaceX awarded resupply contract for Dragon. SpaceX has five Falcon 1 test flights. Falcon 9 engines are ground tested.
2009:
2010: First flight test of Falcon 9 v1.0. Carried stripped down Dragon. Second flight test, COTS Demo Flight 1
2011:
2012: COTS Demo Flight 2+. First resupply mission
2013: Falcon 9 v1.1 demo mission
2014: SpaceX picked for crew transport with Dragon V2
2015: Dragon V2 Pad Abort. Dragon Air Abort
2016: Flight test unmanned
2017: First flight crewed


The timeline is interesting because the request for proposals for both was 2005. However, it could be argued that the period up to 2010 wasted time on the CEV design which was little more than an upgraded Apollo CSM. During the same period SpaceX was getting Dragon in shape. The first flight test with the stripped down Dragon in 2010 was somewhat similar to the Orion EFT-1 test in 2014. Neither of these was the final version of the craft. The main difference is that Dragon had its first flight test the same year whereas Orion's first flight test will be more than 3 years later.

Orion is a larger vehicle, about twice the weight of Dragon. The original plan was for Orion to carry both crew and resupply and be reusable for ISS missions. So, Dragon is designed as reusable. It's heat shield only loses a little bit of its surface during each re-entry from LEO. In contrast, the much higher velocities of a lunar return would not allow reusing the heat shield. The higher velocity also requires more structural strength.

Falcon 9 ran about a year behind schedule for its flight testing. However, Falcon and Dragon together only cost about $850 million to develop. Ares 1 seemed to be a waste of time since the rated payload was already available with Delta IV Heavy. Part of the Constellation program was deceptive. To try to avoid the cost of human rating, Ares V was designated as cargo with Ares 1 carrying the actual crew. In contrast, both SLS and Falcon Heavy will be human rated. Event Atlas V will be human rated.

From engine ground testing to mission readiness was four years with Falcon 9 and Dragon. SLS is ground testing now with crew still six years out. Admittedly, this could probably be moved forward if there was an actual need. Delta IV Heavy, the world's largest lifter, was at its limits with EFT-1. You would probably need Falcon Heavy but it hasn't flown yet.

 

[barehl]

Let's go over the history again.

The Shuttle program was pretty much an upgrade of the Dyna Soar program. Everyone wanted to build shuttles: Soviet Buran, Japanese HOPE, and ESA Hermes. But after losing two Shuttles, these have all been scrapped. The only program still in existence is Dream Chaser which is not funded past early next year. I suppose if it looked promising it might get some support from somewhere. Of course, SpaceShipTwo's failure probably didn't help. The claim now is that the same company that built SpaceShipOne will make a carrier aircraft far larger than the WhiteKnightTwo. This vehicle, the Stratolaunch carrier, would use six 747 engines and have a very large wingspan to take the payload to maximum altitude. Even so, the Dream Chaser craft would have to be scaled down to 75% size. In some ways this is reminiscent of the X-15 flights, except this has been pushed to the limits of practicality.

After the Challenger disaster in 1986, NASA began working on a Shuttle replacement. The vehicle selected in 1996 was Venture Star which was a single-stage-to-orbit space plane with aerospike engines. This was canceled in 2001. A competing STTO design was DC-X. It was noteworthy for being designed to land vertically on legs. Earlier than this was the British HOTOL STTO design which was canceled in 1988. However, this is apparently still alive in an updated version named, Skylon. It was still receiving some funding in 2013. Of course the problem with any STTO design is arriving in orbit with a usable amount of payload.

I understood why NASA chose a similar escape tower for Orion as used for Apollo. I also understand why Apollo wants the Dragon V2 flights to use parachutes and land in water. However, just as the Dragon resupply craft paved the way for Dragon V2 it is possible that a good track record of vertical landing could allow crewed landings the same way. A vertical landing on Earth with rocket power would certainly be interesting (like the early sci fi movies). I suppose this would be a continuation of the DC-X concept but without the STTO handicap. And, there is an obvious side effect to pursuing vertical landing. If you can do it on Earth then you can do it on Mars or the Moon.

The Altair lunar lander in Constellation would have been about 3 times the weight of the Lunar Module used on Apollo. It was supposed to have a duration of up to 210 days. One does have to wonder what there would be to do for 7 months at one location However, topping the unrealistic scale has to be Mars One which seems to have the idea that they could send a crew of four to Mars using a Falcon Heavy. Off the top of my head, I think a Mars transfer payload would only be about 35,000 lbs. A Dragon V2 is 10,000 so that wouldn't leave much for the rest of the ship. I'm not seeing it myself.

 

[Mikemcc]

Don't know about Mars One but the SpaceX plan for Mars is using the Mars Colonial Transporter (MCT) launched by the BFR, both of which only exist as a few briefing notes at present, but will just use improvements on existing technology, nothing wildly new.

Skylon also doesn't exist beyond a few artist and engineering concepts. It depends on the development of the Sabre engine. While that is still promising, it's a long way from any sort of flight capable hardware. Even then it's payload is going to be relatively modest and the initial Skylon plans are that it will be unmanned.

 

[theprestige]

Let's go over the history again.

The Shuttle program was pretty much an upgrade of the Dyna Soar program. Everyone wanted to build shuttles: Soviet Buran, Japanese HOPE, and ESA Hermes. But after losing two Shuttles, these have all been scrapped. The only program still in existence is Dream Chaser which is not funded past early next year.

A history of shuttle programs without the X-37 is a history not worth having.

 

[blutoski]

I was looking at the Dragon V2 mockup and thinking that it looked good enough to use as a movie set. Certainly I don't recall another craft with an exposed geodetic frame or flat screen monitor. The carbon fiber seats aren't too bad either. I assume the look is functional rather than artistic.

This vehicle is getting ready for a static test. Hopefully the first actual test with crash dummies will be before year's end.

I'm pretty sure in 30 years it'll look as dated as a Miami Vice film set.

Word of the day: [Zeerust]

 

[barehl]

A history of shuttle programs without the X-37 is a history not worth having.

Well, the problem is that the X-37B is probably being used as a reconnaissance drone. It doesn't have a crew and it is only half the size of the tiny Dream Chaser. Boeing did a paper proposal of the X-37C version with crew and close to the size of Dream Chaser. However, this was apparently dropped in favor of Boeing's CST-100 craft.

If Boeing was actually serious about a crewed shuttle type vehicle, they could presumably team up with Sierra Nevada and use their considerable X-37 experience to get Dream Chaser off the ground. That isn't happening so X-37 is currently dead-end and Dream Chaser isn't much further along.

 

[barehl]

Don't know about Mars One

http://www.mars-one.com

The Mars Transit Vehicle is a compact space station that will carry the astronauts from Earth orbit to Mars. It is comprised of four parts which are docked in Earth orbit: two propellant stages, a Transit Habitat and a Lander. The propellant stages are used to propel the Transit Vehicle from Earth orbit to Mars

Transit Habitat - 44,000 lbs

Mars Landing capsule: The SpaceX capsule under consideration is a variant of the Dragon Capsule.

Lander - Dragon V2, 10,000 lbs.

Mars One anticipates using Space X Falcon Heavy

The Transit Habitat and Lander would be half the LEO payload of Falcon Heavy which wouldn't leave enough for fuel. However, since it is assembled, you might be able to get enough fuel using two Falcon Heavy launches. However, that lander is not nearly big enough to carry the living spaces and life support systems they would need on the surface. I guess they are aware of that.

Several rocket launches will be needed to take payloads into Earth orbit and then onto Mars.

They plan to set up a colony site before sending humans there. I would hate to guess how many Falcon Heavy launches that would take. I'm thinking a minimum of six and then at least two more for the crew launches.

but the SpaceX plan for Mars is using the Mars Colonial Transporter (MCT) launched by the BFR, both of which only exist as a few briefing notes at present, but will just use improvements on existing technology, nothing wildly new.

We can talk about this. First of all, the rocket will never be named Big Falcon Rocket so the BFR acronym is useless. And saying that it is about briefing notes is ridiculous. Raptor has been in development since 2009 and is currently in component testing at Stennis.

SpaceX's current largest rocket is the Merlin 1D at 160,000 lbs thrust. The older 1C is 140,000. The Falcon Heavy uses three sections with 9 engines each. So, 27 x 160,000 = 4.32 million lbs thrust. To simplify things, SpaceX would like to make a single body rocket with the same lifting capacity as the current Falcon Heavy which would reduce the cost. The target seems to be the same as the Space Shuttle Main engine (RS-25) at 510,000 lbs. So, 9 x 510,000 = 4.59 million lbs thrust. However, you can then stick three of these together like the Falcon Heavy and get 3 x 4.59 million = 13.77 million lbs thrust. This would be larger than NASA's old Nova rocket design which had 12 million lbs thrust. With this much capacity, you could probably put half a million lbs in LEO. And, it is conceivable that you could build a Mars mission with that.

Blue Origin's current BE-3 engine is 110,000 lbs thrust which is a little smaller than SpaceX's old Merlin 1C. However, apparently because Russia's leader has been acting crazy, NASA would like to stop using the Russian RD-180 on Atlas V. Unfortunately, there isn't any replacement engine available at the price point of the RD-180. So, Blue Origin is working on the BE-4 engine which will have 550,000 lbs of thrust. Two of these would have 1.1 million lbs of thrust which is more than the current 860,000 lbs of thrust Atlas V has with RD-180. This would be less capacity than Delta-IV Heavy but also much less cost. This new version of Atlas V would be called Vulcan.

SpaceX's Raptor engine is too large for the test stand they used for Merlin 1D. The E-2 facility at Stennis had to be upgraded to handle methane. This cost about $600,000. When it was finished they had a ribbon cutting ceremony in April 2014.
Participants in the ribbon-cutting ceremony were: Mississippi Gov. Phil Bryant, U.S. Sen. Thad Cochran of Mississippi, SpaceX President and Chief Operating Officer Gwynne Shotwell, U.S. Rep. Steven Palazzo of Mississippi and NASA’s Stennis Space Center Director Rick Gilbrech.

The E-2 testing phase is expected to last 12-24 months. The E-2 stand tops out at 100,000 lbs of thrust so it can only do component testing on Raptor. There has been a recent high demand for test stands at Stennis. The A-1 stand had been setting idle for nearly a decade but was put to use last year to test the J-2X and then was used to test RS-25 engines.

The expendable version of the Space Shuttle Main Engine is RS-25. The SLS will use four of these. The B-2 test stand at Stennis is being upgraded so that it can test four at the same time. It currently stands 61' high but is being extended to 161'. This could be the stand that SpaceX will use. The B-1 stand is leased to Rocketdyne which uses it to test the 660,000 lb thrust RS-68 engine used in Delta IV. The B1/B2 test stands were used for the F-1 engines on Saturn V.

Blue origin just built a new test stand at its Texas facility that can handle LNG and 1 million lbs of thrust. Apparently by using their own facilities they hope to stay ahead of SpaceX. The BE-4 is in component testing right now at Washington and Texas with full engine testing in 2016. Flight testing would be perhaps 2017. SpaceX's Raptor engine should be a little later than this.

*****

One of the problems is that people keep assuming that a Mars Colonial Transport is pie in the sky. It's not but understanding why is a little complicated.

SpaceX started with Merlin 1C which was upgraded to Merlin 1D on Falcon 9. They have been very happy with this program because they managed to undercut the price of the Russian Soyuz. For the engine specifically, they are happy with the thrust to weight, and the cost. They are not as happy with the Isp nor with having to use nine engines. The only way to use fewer engines would be to build a much larger engine. From what I can see, you could build a Falcon 9 with three Raptor engines instead of nine Merlin 1D engines. The issue of Isp is because the Merlin is an open cycle gas generating engine. In other words, the fuel that is burned to power the turbopump is exhausted and therefore contributes nothing to the thrust. To increase the Isp you need a closed cycle engine. The Raptor engine is a closed cycle two stage engine. It has about 14% more Isp than the Merlin.

Is this pie in the sky? No, it's win/win because a successful Raptor engine would let you build a cheaper Falcon 9. Okay, so what about Falcon Heavy? Let's assume that there is a genuine market for Falcon Heavy. The Raptor engine would let you build this rocket with a single stack instead of three stacks. That reduces the cost. It further reduces the cost because of fewer engines and higher Isp. A rocket like this might be useful for launching planetary probes. So, let's assume that you want something bigger. The core is 4.59 million lbs of thrust. The existing Falcon 9 stacks are 1.44 million lbs of thrust. So, strap on two of these as boosters and you get 7.47 million lbs of thrust which is pretty close to Saturn V. That three part stack with 13.77 million lbs of thrust is basically a side-effect. Could this challenge SLS as a launcher? Sure.

However, thinking that this means some kind of colonization project on SpaceX's part is absurd. Right now, they have the Dragon capsule which can double as a lander. They do not have a habitat module or any of the many other things they would need to set up a base on Mars. Nor are they going to be designing these things. Keep in mind that this was the very same company that topped out at Falcon 1 until Obama shifted money to the private sector to fund new development. Without this, there would be no Falcon 9. SpaceX is not going to fund a long duration ship and all the other things that would be needed. And the Mars One program is nothing more than wishful thinking even with a real SpaceX booster. The only source today of long term facilities is the International Space Station. Yes, SpaceX will be happy to put together a lower cost sample return mission for NASA but getting humans to Mars is way beyond their capability.

 

[theprestige]

Well, the problem is that the X-37B is probably being used as a reconnaissance drone.

Even if it were doing reconnaissance*, why is this a problem?

It doesn't have a crew and it is only half the size of the tiny Dream Chaser. Boeing did a paper proposal of the X-37C version with crew and close to the size of Dream Chaser. However, this was apparently dropped in favor of Boeing's CST-100 craft.

Why does the size or crew complement matter? It's a shuttle, and it's doing useful work. I think it's notable that it doesn't need to be big or to be crewed, in order to achieve the purpose of a shuttle craft.

I think you're making a mistake to leave it out of your assessment of the current state of the art in applied shuttle technology. The fact that the US Air Force is currently getting shuttle work done without needing a larger, crewed shuttle should tell you something about the current and future state of play in the field of shuttle operations.

Size is only important to the intended purpose of the space craft. Bigger is only better if bigger is what's actually needed to fulfill the purpose. The same is true for a crew. Why is it important to only consider shuttles that meet some sort of size or crew requirement? Are you making an arbitrary distinction, or a meaningful one?

If Boeing was actually serious about a crewed shuttle type vehicle, they could presumably team up with Sierra Nevada and use their considerable X-37 experience to get Dream Chaser off the ground. That isn't happening so X-37 is currently dead-end and Dream Chaser isn't much further along.

Why on earth should Boeing be serious about a crewed shuttle? Does Boeing need one? Are any of Boeing's customers asking for one? Is there a clear market opportunity for a large crewed shuttle, that Boeing would be wise to exploit?

In what way is the X-37 a dead end? First, it's an operational spacecraft that does what it was designed to do. Second, it's doing useful work. Even if nothing else comes of it, it's already a successful end result in its own right.

Third, it is giving the Air Force operational experience with shuttle craft. Fourth, it is giving the Air Force operational experience with autonomous spaceflight systems. Far from being "dead ends", these are both open paths to future developments and applications.

What if Dream Chaser is the dead end?














*I think the claim that the X-37 is "probably being used as a reconnaissance drone" is implausible, primarily due to its size, but this question has been debated elsewhere on the Forum, and doesn't need to be re-hashed here.

 

[barehl]

Even if it were doing reconnaissance*, why is this a problem?

That's a problem because specialty recon vehicles like U-2 and SR-71 never had to meet realistic standards of operational cost or reliability. General spacecraft do have to meet these standards.

Why does the size or crew complement matter? It's a shuttle, and it's doing useful work. I think it's notable that it doesn't need to be big or to be crewed, in order to achieve the purpose of a shuttle craft.

Because we are talking about human-rated craft. This pretty much requires a human crew.

I think you're making a mistake to leave it out of your assessment of the current state of the art in applied shuttle technology. The fact that the US Air Force is currently getting shuttle work done without needing a larger, crewed shuttle should tell you something about the current and future state of play in the field of shuttle operations.

No, not really. The Air Force can always throw money at a problem. The fact that no country on the planet is currently pursuing a human-rated shuttle craft should tell you something though.

Size is only important to the intended purpose of the space craft. Bigger is only better if bigger is what's actually needed to fulfill the purpose. The same is true for a crew. Why is it important to only consider shuttles that meet some sort of size or crew requirement? Are you making an arbitrary distinction, or a meaningful one?

Well, again, I've only been talking about human-rated vehicles. The Dawn Probe at Ceres is a nice vehicle but it too is unrelated to this discussion.

Why on earth should Boeing be serious about a crewed shuttle? Does Boeing need one? Are any of Boeing's customers asking for one? Is there a clear market opportunity for a large crewed shuttle, that Boeing would be wise to exploit?

The answer to that is probably, no. Again, the fact that NASA did not move Dream Chaser to the next round of funding as it did with Dragon V2 and CST-100 should tell you something.

In what way is the X-37 a dead end? First, it's an operational spacecraft that does what it was designed to do. Second, it's doing useful work. Even if nothing else comes of it, it's already a successful end result in its own right.

Much like SS Great Eastern which successfully laid the transatlantic cable and then was scrapped because it wasn't useful for anything else.

Third, it is giving the Air Force operational experience with shuttle craft. Fourth, it is giving the Air Force operational experience with autonomous spaceflight systems. Far from being "dead ends", these are both open paths to future developments and applications.

This only matters if it becomes human-rated at some point.

What if Dream Chaser is the dead end?

It has been claimed that a 75% scale Dream Chaser will be developed. I guess we'll see.

*I think the claim that the X-37 is "probably being used as a reconnaissance drone" is implausible, primarily due to its size, but this question has been debated elsewhere on the Forum, and doesn't need to be re-hashed here.

It doesn't matter. If it isn't being used for recon then it is just an experimental vehicle and therefore even lower value.

I get that you like the X-37 but if it doesn't lead to something in terms of a general use space craft carrying humans then it isn't important. SpaceX's Dragon resupply craft is similar. The fact that it can haul cargo into space and bring things back is good. But it's only the V2 program as a human rated craft that makes it relevant to this discussion. Orbital Sciences has the similar Cygnus resupply craft but it isn't relevant because it isn't being developed further. However Boeing's CST-100 is relevant because it will be human-rated.

 

[barehl]

I probably have not explained the difference in development very well. It's common for moon hoax enthusiasts to ask why if the F-1 engine was real that we don't still make it today. The answer is the difference between a specialty engine and a general purpose engine. Each F-1 required 20,000 hand welds to form the cooling tubing that runs down the exhaust housing. It worked but it made the engine hard to produce and expensive. When Dynetics looked at resurrecting the engine they immediately looked for ways to make the engine easier to build and cheaper. They looked at reducing the parts count by something like 90%. This is the F-1B design. Instead of cooling tubing, it uses an ablative liner.

The Space Shuttle Main Engine, RS-25D, produced 418,000 lbs of thrust and had to be durable enough for many uses. There will be a cheaper, lighter, expendable version of this engine which will be used on SLS. Yet, when SpaceX needed an engine with similar thrust, they never considered the RS-25 because it isn't cost competitive with their Merlin-1D. Instead, they are developing the Raptor engine with 510,000 lbs of thrust. You would also think that the RS-68 at 660,000 lbs of thrust could have been downgraded to give Blue Origin what they needed. But, again, because the RS-68 is too expensive, they too are developing the BE-4 engine with 550,000 lbs of thrust.

The J-2 engine is also in limbo. It hasn't been produced since Apollo. On the ground it gives about the same thrust as a BE-3. There were plans to upgrade it to 294,000 lbs of vacuum thrust as J-2X and it was even tested at the A-1 stand at Stennis. But that was suspended in 2014. Even SpaceX is planning to use a vacuum version of their Merlin 1D engine to power a Mars sample mission. This engine would be slightly less powerful than the original J-2. With the old Inertial Upper Stage retired along with the Shuttle, the primary rocket used in the US to reach higher orbits or to leave Earth orbit is the RL-10 which is designed to be very efficient in a vacuum. SLS is now planned to use four RL-10 engines to leave Earth orbit instead of the J-2X. Four of these engines were even used on the DC-X vehicle. SpaceX's SuperDraco is in the same class as the RL-10 so presumably they felt that it was too expensive.