Unmanned U.S. Air Force space plane lands after secret, two-year mission • Hacker News Board

Re: Unmanned U.S. Air Force space plane lands after secret, two-year mission

#161

Post by bjd2385 » Mon, May 08, 2017, 7:41 PM UTC

nradov wrote: post #75

bjd2385 wrote: post #16

Earlier quoted context omitted.

Way I see it is, if we can land a rover the size of a minivan on a different planet, we should be able to do this without much more effort. Money, perhaps, yes; but, we've already done it.

You might think so, but the difficulty doesn't scale linearly with size and weight. For example there's a practical upper bound on airbags to absorb landing shock; we can't just build larger ones for a capsule carrying humans.

Not at all what I was referring to in my comment. But, yes, you're entirely accurate regarding the airbags. (:

Re: Unmanned U.S. Air Force space plane lands after secret, two-year mission

#162

Post by gibsjose » Mon, May 08, 2017, 9:11 PM UTC

rootbear wrote: post #148

gibsjose wrote: post #18

Earlier quoted context omitted.

On-orbit satellite servicing and refueling has not been performed as of yet, but we are currently working on it: https://sspd.gsfc.nasa.gov/restore-l.html

I thought Restore-L was one of the missions who's funding was cut in the budget proposal. I'm partly funded by PACE, which is toast.

Turns out we are funded. PACE may be funded as well actually, but there's no clear indication either way. I was at the all-hands a few weeks ago where it seemed to be a bit more grim but lately there has been some talk of PACE surviving.

Re: Unmanned U.S. Air Force space plane lands after secret, two-year mission

#163

Post by gibsjose » Mon, May 08, 2017, 9:24 PM UTC

dogma1138 wrote: post #130

gibsjose wrote: post #102

Earlier quoted context omitted.

Yeah, the SSPD (NASA office behind Restore-L) started with the Hubble reservicing missions

So I think what you meant was, unmanned servicing has not been performed yet?

Yeah, that's more correct

Re: Unmanned U.S. Air Force space plane lands after secret, two-year mission

#164

Post by kobeya » Mon, May 08, 2017, 10:50 PM UTC

zardo wrote: post #153

kobeya wrote: post #133

Earlier quoted context omitted.

It could land directly, yes, but it makes use of the aerobrake for slow-down. Without that aerobrake it would not have enough fuel to do a powered landing all the way down and then return to orbit (I think -- I don't actually work for SpaceX; I'm just a fan). But it is my understanding that it has enough fuel to do a full propulsive landing from orbit and back again, without an aerobrake.

>But it is my understanding that it has enough fuel to do a full propulsive landing from orbit and back again, without an aerobrake. Not even close. Dragon has something like 450m/s of dv to use. Getting from the surface of Mars to orbit takes 3800. Orbital capture requires around 2000m/s. Without aerobraking, it couldn't enter Mars orbit, let alone land.

Are you looking at the CRS dragon specs? It is absolutely the case that future designs of Dragon are able to do a direct powered ascent from Mars. That requires a lot more that 450m/s. Current dragon can't do that, but I wasn't talking about current dragon.

Re: Unmanned U.S. Air Force space plane lands after secret, two-year mission

#165

Post by killjoywashere » Mon, May 08, 2017, 11:12 PM UTC

roryisok wrote: post #128

killjoywashere wrote: post #105

Anyone find it interesting that this thing is landing several days after a North Korean missile failed minutes into flight? Time to re-arm?

Re-arm with what? Bad advice?

Kinetic weapons? Power supply for electronic warfare sources?

Re: Unmanned U.S. Air Force space plane lands after secret, two-year mission

#166

Post by mapt » Mon, May 08, 2017, 11:29 PM UTC

nradov wrote: post #77

mapt wrote: post #66

Earlier quoted context omitted.

The driving requirement of the Shuttle was that it should be feasible to steal a Soviet satellite sporting unknown new orbital technology, before the Soviets had the opportunity to intervene, and that it be prepared to fly fairly quickly whatever its faults to be ready for potential Soviet expansions into spaceflight as an area of competition. There were a lot of other requirements and stakeholders that were part of…

That's completely wrong. There was no serious consideration of stealing Soviet satellites. Everyone knew that we'd never be able to get away with that. The driving requirement was to act as a successor to the SR-71. Launch, make a single reconnaissance pass over the Soviet Union, and then utilize the cross-range capability to land immediately so that the film could be developed. But by the time the Shuttle was actual…

You don't need something a tenth the size of the Shuttle to be an effective manned camera platform, even an effective manned camera platform with extreme cross-range.

We had effective unmanned film camera platforms in space long before we had CCDs, long before the Shuttle was contemplated.

> During the 1950s, a Soviet hoax had led to American fears of a bomber gap. In 1968, after gaining satellite photography, the United States' intelligence agencies were able to state with certainty that "No new ICBM complexes have been established in the USSR during the past year."[10] President Lyndon B. Johnson told a gathering in 1967:

>> I wouldn't want to be quoted on this ... We've spent $35 or $40 billion on the space program. And if nothing else had come out of it except the knowledge that we gained from space photography, it would be worth ten times what the whole program has cost. Because tonight we know how many missiles the enemy has and, it turned out, our guesses were way off. We were doing things we didn't need to do. We were building things we didn't need to build. We were harboring fears we didn't need to harbor.[10]

Re: Unmanned U.S. Air Force space plane lands after secret, two-year mission

#167

Post by pavement » Tue, May 09, 2017, 1:29 AM UTC

nradov wrote: post #147

pavement wrote: post #131

Earlier quoted context omitted.

Kinetic impactors are not missiles. Repeat: Kinetic impactors are not missiles. https://en.wikipedia.org/wiki/Kinetic_bombardment These are not things that get fired. You don't launch them. They don't follow a trajectory. They might just travel straight down from a geostationary orbit, depending on implementation. Yes, a guidance package might be necessary (depending on target discrimination, and precision, which in…

This is 100% wrong. You don't understand orbital mechanics. Everything follows a trajectory until force is applied. When you release something in orbit it doesn't fall down. It continues orbiting until an attached rocket motor does a de-orbit burn. Rocket motors are subject to manufacturing variations plus there are a lot of atmospheric effects on the way down to the surface so any missile would require a sophisticat…

Prove to me that a rocket simply MUST be burnt, to set an orbiting mass in motion.

Propellant is a conventional means, but certainly not the sole means. Magnetic induction could eject a slug from an orbiting platform, or inert gases could jettison to induce motion. Burnt fuel isn't a requirement.

You insist on a rocket motor. But you just resist the idea of this form of orbital weaponry.

A large enough asteroid could enter into earth's gravity well and chart a straight line to impact.

You presume preconceived concept of a weapons platform already in orbit, controlled from the ground, or by a terrestrial entity. But a weapon of lunar origin might insert into the atmosphere differently. As with any weapon, an approach to target should be the least defensible path. After atmospheric re-entry, when position is given away, you'd want the penetrator to travel as perpendicularly to the target as possible, but prior to that moment, any stealthy approach is game.

I'm not 100% wrong. You're 100% obstinate.

Re: Unmanned U.S. Air Force space plane lands after secret, two-year mission

#168

Post by godelski » Tue, May 09, 2017, 2:20 AM UTC

nradov wrote: post #75

bjd2385 wrote: post #16

Earlier quoted context omitted.

Way I see it is, if we can land a rover the size of a minivan on a different planet, we should be able to do this without much more effort. Money, perhaps, yes; but, we've already done it.

You might think so, but the difficulty doesn't scale linearly with size and weight. For example there's a practical upper bound on airbags to absorb landing shock; we can't just build larger ones for a capsule carrying humans.

Not to mention that when you add fuel you now need more fuel for the added mass of that fuel. And....

Re: Unmanned U.S. Air Force space plane lands after secret, two-year mission

#169

Post by nradov » Tue, May 09, 2017, 3:15 AM UTC

pavement wrote: post #167

nradov wrote: post #147

Earlier quoted context omitted.

This is 100% wrong. You don't understand orbital mechanics. Everything follows a trajectory until force is applied. When you release something in orbit it doesn't fall down. It continues orbiting until an attached rocket motor does a de-orbit burn. Rocket motors are subject to manufacturing variations plus there are a lot of atmospheric effects on the way down to the surface so any missile would require a sophisticat…

Prove to me that a rocket simply MUST be burnt, to set an orbiting mass in motion. Propellant is a conventional means, but certainly not the sole means. Magnetic induction could eject a slug from an orbiting platform, or inert gases could jettison to induce motion. Burnt fuel isn't a requirement. You insist on a rocket motor. But you just resist the idea of this form of orbital weaponry. A large enough asteroid could…

You are still 100% wrong. Magnetic induction wouldn't be be practical because it would disrupt the satellite's orbit. Inert gasses are too heavy to be practical for the amount of delta V needed. You're just making things up and missing basic physics concepts.

Re: Unmanned U.S. Air Force space plane lands after secret, two-year mission

#170

Post by nradov » Tue, May 09, 2017, 3:38 AM UTC

mapt wrote: post #166

nradov wrote: post #77

Earlier quoted context omitted.

That's completely wrong. There was no serious consideration of stealing Soviet satellites. Everyone knew that we'd never be able to get away with that. The driving requirement was to act as a successor to the SR-71. Launch, make a single reconnaissance pass over the Soviet Union, and then utilize the cross-range capability to land immediately so that the film could be developed. But by the time the Shuttle was actual…

You don't need something a tenth the size of the Shuttle to be an effective manned camera platform, even an effective manned camera platform with extreme cross-range. We had effective unmanned film camera platforms in space long before we had CCDs, long before the Shuttle was contemplated. > During the 1950s, a Soviet hoax had led to American fears of a bomber gap. In 1968, after gaining satellite photography, the Un…

Yes a manned camera platform could have been much smaller than the shuttle. And the USAF had been designing just such a vehicle until they were forced to consolidate their program with NASA's Shuttle in order to "save money". So we ended up with a compromised vehicle that was too expensive and couldn't do anything very well.