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.
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.
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.
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.
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.
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.
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.
I will still continue to cheer on you bird of choice SKYLON and look forward to her first flight. Like I said, exciting times!
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.
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.
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.
[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.
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.
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
Quote from: john smith 19 on 07/13/2016 09:23 pmA 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).
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?
Quote from: whitelancer64 on 07/13/2016 11:00 pma. 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.
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.
Quote from: john smith 19 on 07/13/2016 11:57 pmYou 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" scenarioAnd 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.
Quote from: whitelancer64 on 07/13/2016 10:22 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?
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.
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.
Quote from: punder on 07/13/2016 11:14 pmQuote from: john smith 19 on 07/13/2016 09:23 pmA 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?
Quote from: strangequark on 07/14/2016 05:29 amQuote from: punder on 07/13/2016 11:14 pmQuote from: john smith 19 on 07/13/2016 09:23 pmA 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?
Quote from: john smith 19 on 07/14/2016 11:18 amBut 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