DC-X: What was the point?

[wumpus]

I've heard a bunch of comments about DC-X, poked through the wiki, and have to ask.  What was the point?

If the point was simply doing basic [rocket] science, then I will simply admit that it did well, and its ideas are bearing fruit.

But it also looks like it was a plan for a real spaceship (presumably a shuttle replacement that we desperately need right now), and I don't think it had a prayer of becoming such.  The real killer is that (at least the wiki claims) that it was supposed to have been a SSTO vehicle.  This has been gone over a few times in this forum, and it just wouldn't work.  The wiki also claimed that it was more an operations project than a technology one (great for NASA, it only took 3 flight controllers).  This makes it clear that there was no real effort to make a "zero dry weight" vehicle needed for SSTO.

On the other hand, that doesn't mean that somebody could have pointed out the obvious "why not make a bigger DC-X as a first stage".  This is pretty much half the concept behind the Falcon (they had a budget of $100M, no real need to get all the way to orbit, and mostly the electronics SpaceX has*).  Of course, if NASA (and congress) had committed to a shuttle replacement, they presumably could have coughed up the funding and the smarts to build an orbital DC-X.

I'm just wondering if there was any idea behind a multiple-stage DC-n or other feasible means to orbit.  Because there was no apparent reason to expect a SSTO to possibly work.

* less than you would think.  Mostly because latency can't get all that much lower while computing a bunch of [unscheduled] things is *much* faster.  Rocket science mostly cares about the latency and getting the answers on time.

[magnemoe]

I thought about an two stage DC-X myself then I heard it was canceled. Same benefit as an falcon9, it would be easier to land because of the wider base, I did not thought about boostback however.
The smaller upper stage would reach orbit and return, I also thought of using an disposable upper stage for heavy payloads. 

And yes trying to make it an SSTO was pretty pointless. I think it was two reasons, first high up people like politicians and generals who think an SSTO would be nice and put up and budget for it who other uses.
Second might be Reagens Star Wars project who to an large degree was an bluff, long term goal was sort of ABM systems. Short term goal was to push Soviet into competing with the US on very high tech areas where they was far less competitive than making tanks, they made their own space shuttle, now have them make an SSTO

 

[mikegarrison]

It was part of SDIO. The "Star Wars" concepts needed a SSTO, so we were developing one. If you take the position that the whole SDIO was just a bluff, then it doesn't matter whether the Delta Clipper would have actually worked or not.

[fredinno]

6 hours ago, wumpus said:

I've heard a bunch of comments about DC-X, poked through the wiki, and have to ask.  What was the point?

If the point was simply doing basic [rocket] science, then I will simply admit that it did well, and its ideas are bearing fruit.

But it also looks like it was a plan for a real spaceship (presumably a shuttle replacement that we desperately need right now), and I don't think it had a prayer of becoming such.  The real killer is that (at least the wiki claims) that it was supposed to have been a SSTO vehicle.  This has been gone over a few times in this forum, and it just wouldn't work.  The wiki also claimed that it was more an operations project than a technology one (great for NASA, it only took 3 flight controllers).  This makes it clear that there was no real effort to make a "zero dry weight" vehicle needed for SSTO.

On the other hand, that doesn't mean that somebody could have pointed out the obvious "why not make a bigger DC-X as a first stage".  This is pretty much half the concept behind the Falcon (they had a budget of $100M, no real need to get all the way to orbit, and mostly the electronics SpaceX has*).  Of course, if NASA (and congress) had committed to a shuttle replacement, they presumably could have coughed up the funding and the smarts to build an orbital DC-X.

I'm just wondering if there was any idea behind a multiple-stage DC-n or other feasible means to orbit.  Because there was no apparent reason to expect a SSTO to possibly work.

* less than you would think.  Mostly because latency can't get all that much lower while computing a bunch of [unscheduled] things is *much* faster.  Rocket science mostly cares about the latency and getting the answers on time.

SSTOs however, theoretically, are cheaper, as you don't need a VAB or integration facilities (aside from payload integration, which can be done on the pad.) You also only need a facility to service one vehicle, not two, as for a two-stage reusable shuttle, or a fully reusable F9.

 

However, the lower efficiency of SSTOs and low performance of reuse to reduce costs so far makes it uneconomical. SSTOs, if pursued, will likely not enter service until the end of the century due to the fact it requires so much lower costs via reuse to be viable.

[Nibb31]

1 hour ago, fredinno said:

SSTOs however, theoretically, are cheaper, as you don't need a VAB or integration facilities (aside from payload integration, which can be done on the pad.) You also only need a facility to service one vehicle, not two, as for a two-stage reusable shuttle, or a fully reusable F9.

Why is that? You still need to integrate and fuel the payload, which needs to be done in a clean environment.

Being SSTO or multi-stage has no bearing on whether it can sleep outside or has to be kept in a hangar. In fact, if your vehicle is reusable, then it must have a TPS, which you will want to protect as much as possible, so it most likely will need a some sort of VAB or maintenance hangar.

And an SSTO must be much larger than a two-stage vehicle with the same payload fraction, you are also going to need a much larger facility than if you had a two stages to cater for. 

 

[Nibb31]

8 hours ago, wumpus said:

I've heard a bunch of comments about DC-X, poked through the wiki, and have to ask.  What was the point?

DC-X was a technological demonstrator for Delta Clipper. It was similar to how X-33 was to be a technological demonstrator for Venture Star. Both DC-X and X-33 were meant to develop the technologies that were required to build a VTVL or VTHL SSTO. However, the main focus wasn't on the SSTO part. It was on reusability and fast-turnaround. In the case of DC-X, the biggest focus was on flight control and powered landing.

I think that merging the two programs (using X-33's composite materials and engine technology and DC-X's layout and flight technology) would have been the best of both worlds and would have been likely to make a good reusable first stage.

Unfortunately, they were both cancelled for political and technical reasons. DC-X was transferred to NASA after SDIO was cancelled, but NASA was reluctant to spend money on it because it competed with their own X-33 program, so they pretty much let it die.

Edited January 29, 2016 by Nibb31

[fredinno]

51 minutes ago, Nibb31 said:

Why is that? You still need to integrate and fuel the payload, which needs to be done in a clean environment.

Being SSTO or multi-stage has no bearing on whether it can sleep outside or has to be kept in a hangar. In fact, if your vehicle is reusable, then it must have a TPS, which you will want to protect as much as possible, so it most likely will need a some sort of VAB or maintenance hangar.

And an SSTO must be much larger than a two-stage vehicle with the same payload fraction, you are also going to need a much larger facility than if you had a two stages to cater for. 

 

Exactly, that's what I meant when I said it would not be worth it until much later. And the hangar used to maintain it is needed anyways, so you can use that instead to keep it in.

[Exoscientist]

16 hours ago, wumpus said:

I've heard a bunch of comments about DC-X, poked through the wiki, and have to ask.  What was the point?

If the point was simply doing basic [rocket] science, then I will simply admit that it did well, and its ideas are bearing fruit.

But it also looks like it was a plan for a real spaceship (presumably a shuttle replacement that we desperately need right now), and I don't think it had a prayer of becoming such.  The real killer is that (at least the wiki claims) that it was supposed to have been a SSTO vehicle.  This has been gone over a few times in this forum, and it just wouldn't work.  The wiki also claimed that it was more an operations project than a technology one (great for NASA, it only took 3 flight controllers).  This makes it clear that there was no real effort to make a "zero dry weight" vehicle needed for SSTO.

On the other hand, that doesn't mean that somebody could have pointed out the obvious "why not make a bigger DC-X as a first stage".  This is pretty much half the concept behind the Falcon (they had a budget of $100M, no real need to get all the way to orbit, and mostly the electronics SpaceX has*).  Of course, if NASA (and congress) had committed to a shuttle replacement, they presumably could have coughed up the funding and the smarts to build an orbital DC-X.

I'm just wondering if there was any idea behind a multiple-stage DC-n or other feasible means to orbit.  Because there was no apparent reason to expect a SSTO to possibly work.

* less than you would think.  Mostly because latency can't get all that much lower while computing a bunch of [unscheduled] things is *much* faster.  Rocket science mostly cares about the latency and getting the answers on time.

 There were considerations towards making a larger DC-X a reusable first stage, as was also the case for the X-33. I was only able to find this image of the X-33 used as a reusable booster, but similar ideas were thought of for the scaled up DC-X:

 

 

  Bob Clark

 

 

[wumpus]

My feeling was that many people pointed to the cancellation of this program as a step backward into space.  What I see is a study in things that might matter for NASA (odd, because it seems to be a DoD program) while kicking the main point (SSTO) down the road.  As far as its cancellation killing a "viable spacecraft", that appears to be mostly wishful thinking.  Regardless of the SSTO mission, going up ~10,000ft (~3,000m) seems little more than what the LEM trainer could do.

In hindsight, it looks like the ideal "lego block" to build an orbital vehicle (mostly just because that's what I've seen recently work, which doesn't mean as much compared to working from first principles).  Just scale one (or more) rockets vastly up to make a first stage (that could land on its own) and land the upper stage as well*.  On the other hand, I'm pretty sure that plenty of early shuttle ideas did the same.  The big advantage "multiple DC-ns" would have over "multiple X-33" would be mounting.  I suspect this advantage might be far big enough for the DC-n to be clearly superior (but it looks like NASA really, really, liked spaceships that looked the "Buck Rodgers" of 1970s TV [looked like airplanes, and landed like airplanes] and not like the "Buck Rogers" of early movies [that looked like V-2s and landed tail first]).

* well, with the type of money Congress is giving the SLS.  Not with the amount of money DC-X got (which was small enough to be under Congressional scrutiny).

[mikegarrison]

I will point out that while airplanes do sometimes live in hangers and usually get maintained in them, a lot of them just park outside. They don't need clean rooms to have cargo loaded into them. We do it out in the rain, snow, etc. You put more fuel in them, top off the potable water, etc. and then take off.

The idea behind the Delta Clipper was that spaceships should work the same way. It lands, you pull the down cargo off and put the up cargo on, you refuel it, and it takes off again. No clean rooms, no VABs, no climate controlled hangers, etc. Whether that idea is realistic or not is highly questionable, but that was the concept they were pushing.

[KerbonautInTraining]

TL;DR

DC-X itself was "just" a smaller version of the grasshopper

[magnemoe]

14 hours ago, Nibb31 said:

Why is that? You still need to integrate and fuel the payload, which needs to be done in a clean environment.

Being SSTO or multi-stage has no bearing on whether it can sleep outside or has to be kept in a hangar. In fact, if your vehicle is reusable, then it must have a TPS, which you will want to protect as much as possible, so it most likely will need a some sort of VAB or maintenance hangar.

And an SSTO must be much larger than a two-stage vehicle with the same payload fraction, you are also going to need a much larger facility than if you had a two stages to cater for. 

 

Clean room is needed for optics, is an high class clean room needed for stuff like communication satellites? Its not used for pods, pointless as you load dirty astronauts into them anyway.
However NASA complained about the lining on the dragon trunk as it used an materiel who could give outgassing and spoil the optic on some instrument to be placed on ISS.
 

6 hours ago, Exoscientist said:

 There were considerations towards making a larger DC-X a reusable first stage, as was also the case for the X-33. I was only able to find this image of the X-33 used as a reusable booster, but similar ideas were thought of for the scaled up DC-X:

 

 

  Bob Clark

 

 

yes, my instinct is to give it an space bay and putt upper stage and cargo in it, drop fairing and wings on upper stage. 
An lifting body reusable upper stage is step 2. 

[fredinno]

10 hours ago, wumpus said:

My feeling was that many people pointed to the cancellation of this program as a step backward into space.  What I see is a study in things that might matter for NASA (odd, because it seems to be a DoD program) while kicking the main point (SSTO) down the road.  As far as its cancellation killing a "viable spacecraft", that appears to be mostly wishful thinking.  Regardless of the SSTO mission, going up ~10,000ft (~3,000m) seems little more than what the LEM trainer could do.

In hindsight, it looks like the ideal "lego block" to build an orbital vehicle (mostly just because that's what I've seen recently work, which doesn't mean as much compared to working from first principles).  Just scale one (or more) rockets vastly up to make a first stage (that could land on its own) and land the upper stage as well*.  On the other hand, I'm pretty sure that plenty of early shuttle ideas did the same.  The big advantage "multiple DC-ns" would have over "multiple X-33" would be mounting.  I suspect this advantage might be far big enough for the DC-n to be clearly superior (but it looks like NASA really, really, liked spaceships that looked the "Buck Rodgers" of 1970s TV [looked like airplanes, and landed like airplanes] and not like the "Buck Rogers" of early movies [that looked like V-2s and landed tail first]).

* well, with the type of money Congress is giving the SLS.  Not with the amount of money DC-X got (which was small enough to be under Congressional scrutiny).

Scaling is actually pretty difficult. Ask Virgin Galactic.

[wumpus]

16 hours ago, fredinno said:

Scaling is actually pretty difficult. Ask Virgin Galactic.

But it's nowhere near the massive scaling (or more likely complete irrelevance of earlier work) for SSTO.

[fredinno]

5 hours ago, wumpus said:

But it's nowhere near the massive scaling (or more likely complete irrelevance of earlier work) for SSTO.

Exactly, scaling a first stage is also very difficult- more so than VG's 'orbiter'.

[tsotha]

DC-X was supposed to be an X program, meaning it was a technology demonstrator.  In X programs, you build a few ships, fly them until you learn what you want to learn, and then shut the program down.  Then you take what you learned and build something that you intend to fulfill mission requirements.

See here for the long version:  http://www.jerrypournelle.com/reports/jerryp/gettospace.html

[magnemoe]

2 hours ago, tsotha said:

DC-X was supposed to be an X program, meaning it was a technology demonstrator.  In X programs, you build a few ships, fly them until you learn what you want to learn, and then shut the program down.  Then you take what you learned and build something that you intend to fulfill mission requirements.

See here for the long version:  http://www.jerrypournelle.com/reports/jerryp/gettospace.html

Good overview of the x-program, however he misses out in the realities of an SSTO, energy needed to fly USA to Australia might be the same but you don't have to bring oxidizer for most of the flight. Neither does the air-frame have to handle orbital reentry. 
Even skylon has an bad payload fraction and that is how well we can do with known technology, we do not know how scramjets will perform in practice but they might be able to handle speeds up to mach 20 and enable orbital burns more like we did in KSP 0.9.