Author Topic: DARPA Experimental Spaceplane 1 (XS-1) Program  (Read 280228 times)

Offline punder

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #520 on: 07/13/2016 11:14 PM »
A VTHL design gives you the worst of both worlds for stresses, needing a shape structure that's strong in 2 axes, one of which has to be phenomenally light to allow takeoff at all.

Agree. Then you add the mass and complication of wings or lifting body along with retractable wheeled landing gear, pretty much useless for anything except recovery. Two private companies are showing, through relatively low-cost programs, that VTVL can work beautifully for a reusable first stage. Still need gear (but much simpler than wheels), but tanks and engines are "dual use" for launch and recovery.

(sp)
« Last Edit: 07/13/2016 11:45 PM by punder »

Offline Darkseraph

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #521 on: 07/13/2016 11:35 PM »
I'm guessing DARPA hopes to reach the moon by shooting for the stars...

They're known for putting forward totally unrealistic challenges beyond the state of the art, wether it is robotic cars or a 100 Year Starship, rather than just applying and refining what we already know how to do.

Just because SpaceX and Blue Origin are pursuing rapidly reusuable rockets doesn't make the DARPA effort pointless. Reducing the costs of access to space will likely benefit from many companies trying many different approaches, not a tiny few.

Just as we don't want all our eggs in one basket on Earth, we ought not to put all them into one technology, person or company. Exciting times are ahead because so many different companies are trying varied and novel approaches to accessing and operating in space. I will be excited to see what works and even what fails!
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." R.P.Feynman

Offline john smith 19

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #522 on: 07/13/2016 11:44 PM »
DARPA's never focused on current technologies. It is always focused on the future, what's next, how to force iteration and innovation of current technologies to provide the capabilites they want to have, but nobody is providing or will likely provide soon.

DARPA, by its nature runs VERY high risk / high reward programs. Their projects often do not succeed... but when they do, they win big.
Exactly.
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SX-1 is not an SSTO. It is a rapidly reusable first stage. Second stage reuse has a fundamental issue with weight for heat shielding and landing legs / gear / fuel cutting into payload capacity which means it is impractical for small to medium sized rockets.
True.
I guess what bothers me is that DARPA is being overly specific about what they want, such as the 10 launches in 10 days, and to me fake requirements breed capabilities that don't match reality - which means the systems could end up being unsustainable (i.e. why not 5 in 10 days, or??).  Not unlike the Shuttle, which was supposedly designed for high reusability, yet there wasn't a need for it's full capabilities.
You can bet the system has been sized for at least one real military requirement. Whether it's identified or classified is another matter.

DARPA is the closest thing to the military giving prizes for innovation. To have a prize contest you obviously need simple, testable criteria so contestants either pass or fail. "high reusability" does not actually mean anything. 10 flights in 10 days does.  Either it can be done by the funded entrant, or it cannot. If so then job done. If not it'll generate a list of "lessons learned" for the next attempt.
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It just seems like DARPA has skipped too far ahead of this issue, and is missing out on surveying WHAT IS POSSIBLE using the technologies that have far less risk.  Especially since they point out that this effort has a TRL of 5, and the X-33 program, which was very challenging, had a TRL of 3.  Plus they don't have much money, which further muddies things.  I think their risk/reward ratio is not right.
Wrong by DARPA's charter the risk/reward ratio ( high/huge) is just right.
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As an example, what if instead of focusing on an SSTO that has a low payload capability, that they focused on using existing reusable stage technology, and added a reusable upper stage?  Which is essentially what Elon Musk had originally hoped he could do with the Falcon family, but I think they found such a capability was a lower priority than the various other efforts they were working.
It's not an SSTO to begin with.

The DC-X was a great demonstrator John, but it never flew it the flight regimes of a Falcon 9R S1. Of  course re-usabilty much less, economic re-usablity has to be proven, as I have been on record as saying. Shapes and structures are all compromises as we know.
At the time the DC-X programme was running the only engine designed for reuse was the SSME. SOP was to both remove dis-assemble after every flight. It was believed impossible to do otherwise. DC-X showed you could re-fly without doing either.  Sponable was looking at these issues long before SX was founded.
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I will still continue to cheer on you bird of choice SKYLON and look forward to her first flight. Like I said, exciting times! :)
Actually I'll support anything that looks like it will substantially lower the $/lb  cost to orbit for a given size of payload, not by increasing the baseline price. When SX were talking fully reusable that was very interesting. Partial reusability looks nowhere near that. Partial reusability for a much smaller payload may deliver it.
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Offline john smith 19

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #523 on: 07/13/2016 11:57 PM »
In this case, I think the scenario is an enemy taking out our orbital intelligence gathering or communications assets. An easy enough thing to do, really. Our military satellites are big, easily tracked, and expensive. And the response I think they think might be best seems to be quickly replacing those assets with a flock of smallsats. This requires having these smallsat assets designed, built, and stockpiled, along with a stockpile of second stages. But that's trivial. What we don't have, and what nobody has, is a booster rocket that can be rapidly deployed and launched on demand repeatedly and economically. I suspect that's the capacity DARPA wants.
You also missed expanding capability of some kind of satellite type over a particular part of the globe for a limited time.  Expanded ELINT, expanded visible or IR imagery, expanded comms channels to support a surge of forces. This is very much the "responsive space" scenario
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Another benefit of this capacity is that even if we aren't attacked, we can retire our big, easily tracked, difficult to replace satellites and economically replace them with smallsats, where if a few get taken out, it's no big loss.
Hmm. Well that's a bit more problematical.

For some tasks bigger is better (anything needing optical lenses) and planners like their big, multi sensor (or multi band) triply redundant birds, even if a multiple, cheaper single task birds would give them a more "granular" capacity, which you could augment as needed.

It's a confidence issue. If  a small (ish) collection of cubesats can really  deliver the resolution of mult metre wide optical mirror then that will change, but it's not going to be an overnight shift.
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Offline Rocket Science

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #524 on: 07/14/2016 12:07 AM »
John, no need to state the obvious, you are preaching to the choir about DC-X... Long live the legend of great Pete Conrad! :)
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Offline Jim

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #525 on: 07/14/2016 12:18 AM »

To expound: DARPA is a military think tank. 200 geniuses in an office building doing nothing but thinking of how to win the next big war.

Urban myth.  That is not what DARPA is.  DARPA employees are not doers, they are funders and project managers.  They have other groups do the work.

Online Coastal Ron

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #526 on: 07/14/2016 12:26 AM »
[SX-1 is not an SSTO. It is a rapidly reusable first stage. Second stage reuse has a fundamental issue with weight for heat shielding and landing legs / gear / fuel cutting into payload capacity which means it is impractical for small to medium sized rockets.

Maybe.  But while some of the images in the article are two-stage systems, some are obviously SSTO.  Maybe artistic license, but that is what I based my comment on.

And with a reusable 1st stage, I think a reusable upper stage is possible.  But is that what DARPA pushing for?
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Jim

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #527 on: 07/14/2016 12:28 AM »

a.  In this case, I think the scenario is an enemy taking out our orbital intelligence gathering or communications assets. An easy enough thing to do, really. Our military satellites are big, easily tracked, and expensive. And the response I think they think might be best seems to be quickly replacing those assets with a flock of smallsats.

b.  This requires having these smallsat assets designed, built, and stockpiled, along with a stockpile of second stages. But that's trivial. What we don't have, and what nobody has, is a booster rocket that can be rapidly deployed and launched on demand repeatedly and economically.

c.  I suspect that's the capacity DARPA wants.

d.  Another benefit of this capacity is that even if we aren't attacked, we can retire our big, easily tracked, difficult to replace satellites and economically replace them with smallsats, where if a few get taken out, it's no big loss.

Not true.

a.  there is are very few types of spacecraft that have small numbers in orbits.  Most are large constellations (GPS) or in GSO (far away but with numbers greater than 5).  WGS and DSCS number over 10, UFO and MUOS more than 10.

b.  No, the issue has been spacecraft readiness.  Boosters have been available but no spacecraft ready to fly.  Even for a simple swap out.  ULA and Spacex could have vehicles ready in 1-2 months from now but there would not be any spacecraft that could take advantage of it.

c.  DARPA doesn't make requirements.

d.  Aside from comsats, most of the spacecraft big because physics requires them to be big.  Resolution requires large apertures.   


Offline Jim

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #528 on: 07/14/2016 12:32 AM »

You also missed expanding capability of some kind of satellite type over a particular part of the globe for a limited time.  Expanded ELINT, expanded visible or IR imagery, expanded comms channels to support a surge of forces. This is very much the "responsive space" scenario


And that is the problem.  Smallsats can't provide that support "over a particular part of the globe for a limited time" except for the first pass (unless in GSO).  Subsequent passes are subject to the same orbital constraints as the existing spacecraft.

Offline strangequark

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #529 on: 07/14/2016 05:29 AM »
A VTHL design gives you the worst of both worlds for stresses, needing a shape structure that's strong in 2 axes, one of which has to be phenomenally light to allow takeoff at all.
Still need gear (but much simpler than wheels).

Do you?

Offline strangequark

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #530 on: 07/14/2016 05:31 AM »
Maybe.  But while some of the images in the article are two-stage systems, some are obviously SSTO.  Maybe artistic license, but that is what I based my comment on.

And with a reusable 1st stage, I think a reusable upper stage is possible.  But is that what DARPA pushing for?

Which ones do you think are SSTO systems?

Offline Chalmer

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #531 on: 07/14/2016 10:41 AM »

a.  In this case, I think the scenario is an enemy taking out our orbital intelligence gathering or communications assets. An easy enough thing to do, really. Our military satellites are big, easily tracked, and expensive. And the response I think they think might be best seems to be quickly replacing those assets with a flock of smallsats.

b.  This requires having these smallsat assets designed, built, and stockpiled, along with a stockpile of second stages. But that's trivial. What we don't have, and what nobody has, is a booster rocket that can be rapidly deployed and launched on demand repeatedly and economically.

c.  I suspect that's the capacity DARPA wants.

d.  Another benefit of this capacity is that even if we aren't attacked, we can retire our big, easily tracked, difficult to replace satellites and economically replace them with smallsats, where if a few get taken out, it's no big loss.

Not true.

a.  there is are very few types of spacecraft that have small numbers in orbits.  Most are large constellations (GPS) or in GSO (far away but with numbers greater than 5).  WGS and DSCS number over 10, UFO and MUOS more than 10.

b.  No, the issue has been spacecraft readiness.  Boosters have been available but no spacecraft ready to fly.  Even for a simple swap out.  ULA and Spacex could have vehicles ready in 1-2 months from now but there would not be any spacecraft that could take advantage of it.

c.  DARPA doesn't make requirements.

d.  Aside from comsats, most of the spacecraft big because physics requires them to be big.  Resolution requires large apertures.

Given Jims response here, I am now even more baffled about the XS-1 program.

Jim, can you enlighten us all abit about why DARPA is doing this? If you know that is.

What is the capability they are looking for? And why cant hopefully soon to be ready small launcher companies like RocketLab with  Electron, FireFly alpha or even Virgin Galactic with Launcher One not provide that capability?

Offline john smith 19

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #532 on: 07/14/2016 11:18 AM »
b.  No, the issue has been spacecraft readiness.  Boosters have been available but no spacecraft ready to fly.  Even for a simple swap out.  ULA and Spacex could have vehicles ready in 1-2 months from now but there would not be any spacecraft that could take advantage of it.
This raises 2 very interesting points.

The first would be is 2 months short enough the timescales over which the DoD would want it's capabilities increased? If so then clearly further work in this field is unnecessary.

Unfortunately I don't think it is. According to Wikipedia top speed for a Nimitz class carrier is 30 Knots. With the Earth's circumference at 21639 nm it would take it just over 15 days to go half way around the world. A modern large container ship is about 2/3 that and air delivery by C17 would be considerably faster in loads of up to 77 tonnes.

So situations can develop faster and be responded to faster than conventional rockets can deliver new assets to space. Some sort of launch-on-demand system is needed.

Your second point is where it gets really interesting.  This implies that it's not the technology that's the problem, it's the logistics of the supply chain. That suggests 2 options.
1) Stockpiling multiple different kinds of complete satellites for the various tasks.
2)Modular payloads on a bus that can combined in any combination at short notice.

1) is going to be very expensive and you always run the risk of being short the one kind of payload you want and holding a bunch of a kind you don't need.

2)Has more subtle problems. The classic being the coupled loads analysis needed to stop the payload triggering destructive resonances in the LV structure and vice versa. The number of possible module permutations to make up a satellite-on-demand (number of module types ^ number of module slots roughly) would be huge.

Either all would have to be checked before hand so users would know they could snap together any combination with confidence or you have greatly streamline the CLA process and incorporate resonance control features in the design. apart from anti shock mounting on the payload I'm thinking standard points where you could fasten weights, Structural rods where other rods or plates can be screwed to stiffen that member and shift the whole structures resonance spectrum.

I suspect that one of the toughest parts of making this scheme work is for people to accept "good enough" now rather than perfect after several more simulation runs.

You also missed expanding capability of some kind of satellite type over a particular part of the globe for a limited time.  Expanded ELINT, expanded visible or IR imagery, expanded comms channels to support a surge of forces. This is very much the "responsive space" scenario


And that is the problem.  Smallsats can't provide that support "over a particular part of the globe for a limited time" except for the first pass (unless in GSO).  Subsequent passes are subject to the same orbital constraints as the existing spacecraft.
True. As you say to deliver fixed increased capability over a region means a GSO payload.

But smallsats mean that a relatively small LV can now deploy a LEO constellation in one launch to deliver continuing capability over that area as they rise and set over the regions local horizon, as well as all areas along their orbital track.

No I would not say this is a cost effective solution long term but that's not the point. The goal is quick response to sudden threats which can be resolved and the space assets left to reenter when their job is done.
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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #533 on: 07/14/2016 03:39 PM »
[SX-1 is not an SSTO. It is a rapidly reusable first stage. Second stage reuse has a fundamental issue with weight for heat shielding and landing legs / gear / fuel cutting into payload capacity which means it is impractical for small to medium sized rockets.

Maybe.  But while some of the images in the article are two-stage systems, some are obviously SSTO.  Maybe artistic license, but that is what I based my comment on.

And with a reusable 1st stage, I think a reusable upper stage is possible.  But is that what DARPA pushing for?

None of them are SSTO. The images simply do not show the second stage. The XS-1 requirements make this very clear, the program is for a rapidly reusable booster with a small, expendable second stage.
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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #534 on: 07/14/2016 03:44 PM »

a.  In this case, I think the scenario is an enemy taking out our orbital intelligence gathering or communications assets. An easy enough thing to do, really. Our military satellites are big, easily tracked, and expensive. And the response I think they think might be best seems to be quickly replacing those assets with a flock of smallsats.

b.  This requires having these smallsat assets designed, built, and stockpiled, along with a stockpile of second stages. But that's trivial. What we don't have, and what nobody has, is a booster rocket that can be rapidly deployed and launched on demand repeatedly and economically.

c.  I suspect that's the capacity DARPA wants.

d.  Another benefit of this capacity is that even if we aren't attacked, we can retire our big, easily tracked, difficult to replace satellites and economically replace them with smallsats, where if a few get taken out, it's no big loss.

Not true.

a.  there is are very few types of spacecraft that have small numbers in orbits.  Most are large constellations (GPS) or in GSO (far away but with numbers greater than 5).  WGS and DSCS number over 10, UFO and MUOS more than 10.

b.  No, the issue has been spacecraft readiness.  Boosters have been available but no spacecraft ready to fly.  Even for a simple swap out.  ULA and Spacex could have vehicles ready in 1-2 months from now but there would not be any spacecraft that could take advantage of it.

c.  DARPA doesn't make requirements.

d.  Aside from comsats, most of the spacecraft big because physics requires them to be big.  Resolution requires large apertures.

The military has been expressing a general desire for a while to move towards smaller, less expensive satellites. I think this is an enabler for that. It also allows for a rapid and tactical response in the event of a military satellite loss.

Some satellites can't be smaller, that's true, but if a big one is lost, a temporary flock of LEO smallsats could at least give the military some data until a true replacement can be procured / launched.
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Offline john smith 19

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #535 on: 07/14/2016 09:32 PM »
The military has been expressing a general desire for a while to move towards smaller, less expensive satellites. I think this is an enabler for that. It also allows for a rapid and tactical response in the event of a military satellite loss.
Some parts of the military have, others have been content to stay with the traditional "big bird" approach.
Quote
Some satellites can't be smaller, that's true, but if a big one is lost, a temporary flock of LEO smallsats could at least give the military some data until a true replacement can be procured / launched.
The joker in the pack are the trade offs needed to make the concept work. Unless the satellite it's replacing is already in LEO to meet the size, weight and power requirements you're going to have to have multiple replacements in a mini constellation, each with a shorter fractional duty cycle than the larger, higher altitude satellites they replace.
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Offline Jim

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #536 on: 07/14/2016 11:18 PM »

But smallsats mean that a relatively small LV can now deploy a LEO constellation in one launch to deliver continuing capability over that area as they rise and set over the regions local horizon, as well as all areas along their orbital track.

No I would not say this is a cost effective solution long term but that's not the point. The goal is quick response to sudden threats which can be resolved and the space assets left to reenter when their job is done.

No, it can't deploy a constellation.  As I said, just a few spacecraft that will have their first pass of the site.  A constellation requires multiple launches

Offline punder

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #537 on: 07/14/2016 11:33 PM »
A VTHL design gives you the worst of both worlds for stresses, needing a shape structure that's strong in 2 axes, one of which has to be phenomenally light to allow takeoff at all.
Still need gear (but much simpler than wheels).

Do you?

Well, you at least need structure strong and rugged enough to take the weight and survive off-nominal touchdowns. Fins a la Destination Moon? Or a "catcher" system. Or something. What are you suggesting, Oh Mysterious One?  :)

Offline PhotoEngineer

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #538 on: 07/15/2016 06:54 PM »
A VTHL design gives you the worst of both worlds for stresses, needing a shape structure that's strong in 2 axes, one of which has to be phenomenally light to allow takeoff at all.
Still need gear (but much simpler than wheels).

Do you?

Well, you at least need structure strong and rugged enough to take the weight and survive off-nominal touchdowns. Fins a la Destination Moon? Or a "catcher" system. Or something. What are you suggesting, Oh Mysterious One?  :)

Pay no attention to the man behind the curtain :)

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #539 on: 07/16/2016 04:42 PM »

But smallsats mean that a relatively small LV can now deploy a LEO constellation in one launch to deliver continuing capability over that area as they rise and set over the regions local horizon, as well as all areas along their orbital track.

No I would not say this is a cost effective solution long term but that's not the point. The goal is quick response to sudden threats which can be resolved and the space assets left to reenter when their job is done.

No, it can't deploy a constellation.  As I said, just a few spacecraft that will have their first pass of the site.  A constellation requires multiple launches

So that might mean they want a system that can, say, do ten launches in ten days?
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