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

reuters.com

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

#151

Post by nradov »

daemin wrote: post #140
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…

If the Russian satellite is a secret, and the Americans steal it secretly, then of course they would get away with it. It's like a thief stealing from another thief.

There were no secret satellites. Nothing can hide in orbit. Even amateur astronomers are able to track military satellites.

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

#152

Post by nradov »

daemin wrote: post #141
rocqua wrote: post #134

Earlier quoted context omitted.

> They don't follow a trajectory. They might just travel straight down from a geostationary orbit That's not how orbiting works. If you want your projectile to travel straight down, you need to cancel all it's orbital velocity. For geostationary orbit, that's 3km/s of delta V needed. Obviously, you can de-orbit with less delta-V, but then guidance starts becoming necessary. > The slug is simply released with no indic…

I am wondering, what kind of impact would the wind have on these projectiles? Or even on ballistic missiles? I would imagine a nuke having such a large explosion that missing the target by a kilometre won't matter too much. But with a kinetic projectile that kind of deviation would not be acceptable (unless we are talking about seriously big projectiles, like in Tunguska etc).

Wind and other transient atmospheric conditions have a major effect. That's why individual unguided projectiles can't reliably hit a target more than about 4 miles away, and even at that range you have to be really lucky. The range from LEO to surface is a lot longer.

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

#153

Post by zardo »

kobeya wrote: post #133
dotancohen wrote: post #119

Earlier quoted context omitted.

Are you sure about the orbit? Could a Red Dragon not land directly from a Hohmann transfer?

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.

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

#154

Post by zardo »

dotancohen wrote: post #125
kirrent wrote: post #123

Earlier quoted context omitted.

Wikipedia seems to imply that the plan for Red Dragon is a direct atmospheric entry. It makes sense, they don't have a second stage that would last long enough to get there. They don't have the delta-V to get the second stage into a mars transfer with a huge amount of fuel and I doubt there's much utility in spending the 2.3km/s (or thereabouts) of delta-v in getting from the Mars transfer to a low Mars orbit when yo…

There is no dichotomy in aerobraking vs orbit. In fact, I believe most interplanetary orbiters (Galileo, Cassini) used aerobraking to achieve orbit.

They didn't. Aerocapture has only ever been done on Earth.

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

#155

Post by zardo »

kobeya wrote: post #87
taneq wrote: post #63

Earlier quoted context omitted.

I don't understand how they can conclude that "the Dragon-2 has enough power and fuel to land and ascend back to lunar orbit" based only on a comparison of maximum thrust and a statement that the Dragon has an automated landing system. At the very least, they'd need to consider the dry weight and fuel load to make a fair comparison - maybe they did so offscreen but it's not mentioned anywhere in the post.

Because it was a design requirement of the Dragon. It was designed to do that.

It definitely was not designed to de-orbit and land on the moon. It has nowhere near enough dV to do that.

Maybe it has been designed to work as a technology platform for deriving a lunar lander. But the Dragon 2 design is just not capable of doing it, not even close.

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

#156

Post by trafficlight »

kirrent wrote: post #121
kobeya wrote: post #86

Earlier quoted context omitted.

No, powered landings all the way down. At least on the Moon and Mars (from orbit). With more fuel you could do the same from Earth, but why bother?

Dragon is barely capable of landing on the moon if you remove the heat shield and replace it with more fuel and fit additional fuel storage in the capsule. Its powered descents on Mars would only be possible because of atmospheric drag.

It's almost as if it weren't designed to land on the moon.

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

#157

Post by jessriedel »

blackguardx wrote: post #99
jessriedel wrote: post #94

Earlier quoted context omitted.

> Not using fuel while landing saves precious cargo capacity Those wings are also a lot of mass, and hence take away from payload. In fact, propulsive landing always takes less mass than wings in the limit of large craft size. (You can see this by taking an equivalent limit, the limit of thin atmosphere; for sufficiently thin atmosphere, the amount of surface area you need to brake diverges but the amount of fuel to…

I won't argue with that, but that isn't true in the case of the X-37, which is why it glides into landing. Elegance in engineering is fulfilling the requirements in the simplest, cheapest way possible.

Yea, I'll withdraw "inelegant" from my original comment, since I was mostly intending to dispute (concurring with colordrops) the suggestion by Animats that wings are more advanced than capsules. ("It's time to get past capsules".) I wouldn't say the shuttle was a pillar of elegance, but I'm happy to agree that wings can be elegant on the right spacecraft (although, as I alluded to, the intuition that they are less wasteful than consuming fuel can be a bit misleading).

Thanks for your comments.

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

#158

Post by lanbanger »

justin66 wrote: post #40
azinman2 wrote: post #10

Earlier quoted context omitted.

Is it all combusted perfectly, or do they lose some and just leave droplets of toxic liquid propellant in their paths as they fly?

There was at least one mishap during Apollo capsule reentry where astronauts were exposed to fumes from hypergolic fuel, after forgetting to purge the thrusters at the proper time: https://en.wikipedia.org/wiki/Apollo%E2%80%93Soyuz_Test_Proj... That brief exposure, before they got their oxygen masks on, put them in the hospital for a couple of weeks. It really could have been worse. I believe the technical procedure…

Also the Titan II missile explosion at Damascus in 1980: https://en.wikipedia.org/wiki/1980_Damascus_Titan_missile_ex...

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

#159

Post by Diederich »

robotresearcher wrote: post #103
Diederich wrote: post #93

Earlier quoted context omitted.

https://youtu.be/1_FXVjf46T8 Work in progress..Well along in progress.

Oh that was cool. I have a stupid grin on my stupid face now.

It really is....I'm such a SpaceX nut. (:

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

#160

Post by ethbro »

zardo wrote: post #154
dotancohen wrote: post #125

Earlier quoted context omitted.

There is no dichotomy in aerobraking vs orbit. In fact, I believe most interplanetary orbiters (Galileo, Cassini) used aerobraking to achieve orbit.

They didn't. Aerocapture has only ever been done on Earth.

Now I'm curious to run the numbers on how lenient the window is for (I'd assume it would have to be) single pass aerocapture on Mars.

And especially interested on what the options for the problem scenarios look like (e.g. burning off too much or not enough velocity).

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