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US Space Force reveals first look at secretive X-37B space plane in orbit

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Re: US Space Force reveals first look at secretive X-37B space plane in orbit

#91

Post by Rebelgecko »

justahuman74 wrote: post #33
samplatt wrote: post #23

Earlier quoted context omitted.

With a far point so far away from Earth it also means that it requires only tiny amounts of fuel for major orbit changes.

My orbital mechanics is (like most people) weak, is this intended as a generalized physical threat to other satellites?

If you can easily adjust your orbit, it's easy to see lots of places on the earth, or tweak what time you will be over a part of the earth (eg if you want to look at something whose owners know to hide it when satellites are overhead)

Re: US Space Force reveals first look at secretive X-37B space plane in orbit

#93

Post by dylan604 »

psunavy03 wrote: post #82
walrus01 wrote: post #7

Earlier quoted context omitted.

a pretty good satire of the whole thing: https://en.wikipedia.org/wiki/Space_Force_(TV_series)

There were legitimate reasons for spitting USSF as its own service. The only reason people made fun of it was because Trump signed the order for it.

That was not the only reason, but for one that says that they will probably not accept the other reasons.

Re: US Space Force reveals first look at secretive X-37B space plane in orbit

#94

Post by dredmorbius »

Robelius wrote: post #59
dredmorbius wrote: post #32

Earlier quoted context omitted.

As well as change orbital characteristics (apogee, perigee, inclination) at reasonably low cost, enabling closer observation of specific portions of Earth, or of objects in space. Burns at closest approach (perigee) have the largest influence on total orbital characteristics. Burns at furthest approach (apogee) can raise the entire orbit if desired. (Or so I understand.)

Could another benefit be the ability to change payloads? If there was a desire to change the orbits and payloads, then could these serve a function as a more responsive version of existing satellites?

I'm not sure what you mean here.

The US Space Shuttle could similarly "change payloads", with its modular payload bay capable of carrying either one-time cargoes (often satellites for launch), or reusable modules such as Spacelab, parts of which flew on a total of 35 Shuttle missions.

https://en.wikipedia.org/wiki/Spacelab>

But modularity is also inherent in conventional rocket-based launches, with cargoes fitting within the fairing bay capable of being deployed or orbited.

Changing payloads in space is a rather different prospect, though the ability to rendezvous with, take on-board, and de-orbit satellites (man-made or artificial, the US's own, or other nations') is another possible capability. The X37's small size gives only limited potential here, and I'm pretty sure that if the US were snatching other nations' satellites we'd have heard about it.

Re: US Space Force reveals first look at secretive X-37B space plane in orbit

#95

Post by jjk166 »

s1artibartfast wrote: post #84
jjk166 wrote: post #81

Earlier quoted context omitted.

> It you can shoot a satellite at 8 km/s, you probably can also shoot it at 11 km/s. Assuming all else is equal (same altitude, same targeting capability, same flight characteristics), an interceptor for an 11 km/s target needs about 89% more kinetic energy than an interceptor for an 8 km/s target. Realistically, between the rocket equation and atmospheric effects, the faster interceptor would likely need to be far l…

I dont think that it is correct to assume your interceptor needs to match velocity. Any speed will do if you can intercept it on approach instead of chase it down.

I'm not assuming the interceptor needs to match velocity. There is some point you detect the target x1, and some range for your missile from your position x0 to an interception point x2. Your interceptor needs to get from x0 to x2 by the time the time the target gets from x1 to x2. If your target is travelling 37.5% faster, you have 27.2% less time to get to the interception point, which means that you need to fly 37.5% faster, which requires 89% more kinetic energy, regardless of what the baseline speed required was. Alternatively you need to detect things from further away or fire from a closer distance, both of which pose their own issues.

Re: US Space Force reveals first look at secretive X-37B space plane in orbit

#96

Post by bagels »

jjk166 wrote: post #81
credit_guy wrote: post #76

Earlier quoted context omitted.

> But maybe it's zipping too fast there to be easily shot down? A satellite in LEO already has a speed of about 8 km/s. The highest speed of a satellite in a highly elliptical orbit is 11 km/s. It you can shoot a satellite at 8 km/s, you probably can also shoot it at 11 km/s. The problem is, of course, that the perigee of a satellite in a highly elliptical orbit can be over a different part of the planet than your SA…

> It you can shoot a satellite at 8 km/s, you probably can also shoot it at 11 km/s. Assuming all else is equal (same altitude, same targeting capability, same flight characteristics), an interceptor for an 11 km/s target needs about 89% more kinetic energy than an interceptor for an 8 km/s target. Realistically, between the rocket equation and atmospheric effects, the faster interceptor would likely need to be far l…

I don't think that is quite right. You can hit a satellite with a suborbital projectile. The kinetic energy of the satellite is enough on its own if you hit it.

Re: US Space Force reveals first look at secretive X-37B space plane in orbit

#97

Post by credit_guy »

jjk166 wrote: post #95
s1artibartfast wrote: post #84

Earlier quoted context omitted.

I dont think that it is correct to assume your interceptor needs to match velocity. Any speed will do if you can intercept it on approach instead of chase it down.

I'm not assuming the interceptor needs to match velocity. There is some point you detect the target x1, and some range for your missile from your position x0 to an interception point x2. Your interceptor needs to get from x0 to x2 by the time the time the target gets from x1 to x2. If your target is travelling 37.5% faster, you have 27.2% less time to get to the interception point, which means that you need to fly 37…

That's not quite correct, is it? Consider shooting at a bird. A falcon travels twice as fast as a pigeon, but you don't need a bullet that is twice as fast to shot the falcon. You simply adjust the lead distance when you shoot at the falcon. In your argument you assume that you need to cover some distance in the same amount of time, but you don't need to. You simply lead the target a bit more. As for detection time, well, it is basically a guarantee that whoever is considering shooting at a space plane, has the tracking capabilities to know its position at all times. If they don't, they probably can find some reddit where people do that out in the open.

Re: US Space Force reveals first look at secretive X-37B space plane in orbit

#98

Post by s1artibartfast »

credit_guy wrote: post #97
jjk166 wrote: post #95

Earlier quoted context omitted.

I'm not assuming the interceptor needs to match velocity. There is some point you detect the target x1, and some range for your missile from your position x0 to an interception point x2. Your interceptor needs to get from x0 to x2 by the time the time the target gets from x1 to x2. If your target is travelling 37.5% faster, you have 27.2% less time to get to the interception point, which means that you need to fly 37…

That's not quite correct, is it? Consider shooting at a bird. A falcon travels twice as fast as a pigeon, but you don't need a bullet that is twice as fast to shot the falcon. You simply adjust the lead distance when you shoot at the falcon. In your argument you assume that you need to cover some distance in the same amount of time, but you don't need to. You simply lead the target a bit more. As for detection time,…

Agreed, it all depends on the use case. If you are trying to hit an evading target, you have to be faster. If you are trying to deny the ship from a destination, you don't.

Re: US Space Force reveals first look at secretive X-37B space plane in orbit

#99

Post by jjk166 »

credit_guy wrote: post #97
jjk166 wrote: post #95

Earlier quoted context omitted.

I'm not assuming the interceptor needs to match velocity. There is some point you detect the target x1, and some range for your missile from your position x0 to an interception point x2. Your interceptor needs to get from x0 to x2 by the time the time the target gets from x1 to x2. If your target is travelling 37.5% faster, you have 27.2% less time to get to the interception point, which means that you need to fly 37…

That's not quite correct, is it? Consider shooting at a bird. A falcon travels twice as fast as a pigeon, but you don't need a bullet that is twice as fast to shot the falcon. You simply adjust the lead distance when you shoot at the falcon. In your argument you assume that you need to cover some distance in the same amount of time, but you don't need to. You simply lead the target a bit more. As for detection time,…

In this scenario increasing lead distance is equivalent to detecting and firing earlier (ie increasing distance between x1 and x2), which again has serious technical issues. Yes you can hit a falcon with the same bullet, but it's harder to hit. And the big difference in these scenarios is that the bullet is moving much faster than either the pigeon or the falcon, which means you can always buy more time for the falcon to get to the interception point by taking a less efficient path, whereas for the satellite interception where your interceptor is slower than the target, there is some optimal path (basically straight up from right below perigee) that sets a hard limit on how long it takes to get to any interception point.

If your interception point is say 500 km straight up from your launch point, just to get there you need a rocket that rapidly accelerates to over 3 km/s, and it takes a little over 5 minutes to get to the interception point. To hit an 8 km/s target, you need to fire when it is 2500 km away, to hit an 11 km/s target you need to fire when it is 3500 km away. If to score a hit you need to be within 10 meters of the target at interception, then you need to know the position and velocity of the 8 km/s target to within 4 ppm, you need to know it with an accuracy within less than 3 ppm. And note, if you are shooting from 15 km up in a fighter jet, the 8 km/s target is within your radar horizon, the 11 km/s target is not. Not to say that you couldn't build a system with target sharing and more precise tracking, but it would be a different system than the one you need for the less challenging use case.

Now it's not a strictly either or thing. You could use a missile with intermediate speed and fire it less early. There's a whole continuum of solutions, but it will always be harder to hit the faster moving target. And of course you have real world things to consider like if the target has any maneuverability or countermeasures and how much variation in conditions you can afford. Generally you are already using the best targeting system you can get and are already in the most advantageous position you can be in, so the knob you can turn is "how big of a missile do I need to get the performance I require?"

Re: US Space Force reveals first look at secretive X-37B space plane in orbit

#100

Post by jjk166 »

bagels wrote: post #96
jjk166 wrote: post #81

Earlier quoted context omitted.

> It you can shoot a satellite at 8 km/s, you probably can also shoot it at 11 km/s. Assuming all else is equal (same altitude, same targeting capability, same flight characteristics), an interceptor for an 11 km/s target needs about 89% more kinetic energy than an interceptor for an 8 km/s target. Realistically, between the rocket equation and atmospheric effects, the faster interceptor would likely need to be far l…

I don't think that is quite right. You can hit a satellite with a suborbital projectile. The kinetic energy of the satellite is enough on its own if you hit it.

It's not about energy required to destroy it, it's about speed required to get to it.
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