ISV orbit mechanics?

[Unil Makto]

Hey guys, I've been thinking about this for a while now and would love to hear your thoughts as well - how does the ISV implement the rules of orbit mechanics?

1. How does it slow itself down for orbit insertion? I doubt a vehicle of its size could simply rotate 180 degrees and do a retro-burn?

2. What type of orbit does it maintain, and more importantly HOW does it maintain it, reaction jets wouldn't be of much use in this case and besides factoring in all the moons and Polyphemus, I would imagine that corrections would need to be made pretty much every couple of cycles.

3. How does it achieve escape velocity? A running orbit wouldn't quite work here I imagine, because of the celestial arrangement.

What are your thoughts?

[Unil Makto]

Oh and another side-question. How does a craft the size of the Valkyrie shuttle manage re-entry? (Note Pandora's dense atmosphere).

[MarkD]

Well from looking at the ISS- International Space Station. The ISV would use gyroscopes and small thrusters to maneuver in orbit. I saw this once on NASA TV watching a shuttle undocking from the station. "Atlantis be advised Station in motion." and slowly the station began to rotate from the direction it was facing to 90 degrees off of that position.

For orbital mechanics look at http://en.wikipedia.org/wiki/Low_Earth_orbit

To escape velocity, well like present day NASA probes they use another planet's gravity to sling shot at a faster speed. My guess is when ready to leave, the ISV swings around the massive Polyphemus and uses that planet's gravity to go back into deep space.

As to the Valkyrie, it would behave like the real space shuttle. I did read recently it has carbon fiber in the thermal protection system. One error with it is the tiles. The black tiles are understandable,but the white areas could have insulation fabric/ blankets. The space shuttle uses these blankets to replace the white tiles to also reduce weight of the vehicle and increase payload capacity. For example look at http://www.spaceflightnews.net/special/shuttle/sts-122/images/020908/211216main_0209_02_OMS_blanket_comparison.jpg You can see the larger blanket patches compared to the tiles. The dense and reinforced carbon fiber tiles probably help with Pandora's atmosphere. They are a lot stronger than the shuttle tiles used now and more like steel in toughness. The shuttle tiles of today are more like glass-break easily. The Valkyrie's advanced composite structure also helps. I mean who knows where advanced composites will be in the future. You'd probably have stuff that far exceed metals and concrete.

[Unil Makto]

The ISV would use gyroscopes and small thrusters to maneuver in orbit.
That's the thing, would reaction jets still be useful on a vehicle with that size and geometry?


To escape velocity, well like present day NASA probes they use another planet's gravity to sling shot at a faster speed. My guess is when ready to leave, the ISV swings around the massive Polyphemus and uses that planet's gravity to go back into deep space.
Yep, that's what I meant by a running orbit, however bearing in mind the proximity of Polyphemus, would that still be a valid solution? Most likely the ISV would have to enter an orbit around Polyphemus (something like a Hohmann transfer approach)


I mean who knows where advanced composites will be in the future. You'd probably have stuff that far exceed metals and concrete.
Very good point. But still re-entry in such a dense atmosphere (factor in its composition as well) would create an incredible inferno.

[MarkD]

Well the gyroscopes would work just as well, same with the thrusters on the ISV. The gyroscopes are useful if you want to save fuel. I believe it would work. As long as it's slow. For the ISV the gyroscopes would work for large changes in direction, thrusters for tiny changes.

Yes, most likely that would be the case. Also what about aero braking? Many Mars orbiters do this to slow down. http://en.wikipedia.org/wiki/Aerobraking

Well for reentry, it would. Still Pandora is nothing compared to the atmosphere of Venus, with 90 times the pressure of Earth's atmosphere. A few spacecraft survived that inferno and landed safely. Still Venus' toxic acid clouds, rain, and high temprature killed the probes after a few minutes. Venus' surface is hot enough to melt steel. The probes survived landing only because they were built with titanium. Pandora would be easier to land on.

The advanced thermal protection on the Valkyrie would probably withstand 4,000 degrees F. or more. Keeping in mind what I said on composites, who knows what will result. Also the angle would have to be with nose up to 40 degrees to keep entry safe. Not to mention the S turns to bleed off speed. The space shuttle does this during entry for that reason.

[Unil Makto]

Well the gyroscopes would work just as well, same with the thrusters on the ISV. The gyroscopes are useful if you want to save fuel. I believe it would work. As long as it's slow. For the ISV the gyroscopes would work for large changes in direction, thrusters for tiny changes.
Sound plausible, but whatever the implementation it would have to be quite energy-efficient, the only problem I'm having with the truster approach would be that the propellant would have to come from a renewable onboard source, simple dump methods aren't likely to work because of the potentially huge number of corrections required.


Also what about aero braking?
I did not consider this to be honest. Thanks.


. A few spacecraft survived that inferno and landed safely.
Granted, but consider their size and shape. The shuttle just screams "I'm a match" with that over-wing design. Just consider the surface area you're going to have for re-entry. You'll get trapped layers underneath, and around the fuselage. And the inlet vents pretty much defeat any thermal control measures. But one thing's certain with all that xenon and methane in the atmosphere it is going to be an incredible light show!



lso the angle would have to be with nose up to 40 degrees to keep entry safe. Not to mention the S turns to bleed off speed.
40 degree angle with that wing area...those composites better be tough!

Still Venus' toxic acid clouds, rain, and high temprature killed the probes after a few minutes. Venus' surface is hot enough to melt steel.
There was a pretty good artist's impression on what the surface might look like. I'll try to find it and will scan it.

[MarkD]

The thruster pulses would be tiny anyway. Not much to move a massive ship.

No problem.

Well the Venus probes just drop in like a rock. The Valkyrie and space shuttle pretty much glide into the atmosphere at that angle. Peak heating would be at 200,000 feet. The engine locations on the Valkyrie would have gap fillers to seal the seam between the engine or landing gear door panels and the rest of the vehicle. As long as there are no gaps or damage to the heat shield, it will survive.

[Unil Makto]

Peak heating would be at 200,000 feet.
That is assuming an Earth-like atmosphere though The model on Pandora would be quite weird I suppose, due to the abnormal magnetic activity and chemical structure of the atmosphere.


he engine locations on the Valkyrie would have gap fillers to seal the seam between the engine or landing gear door panels and the rest of the vehicle.
Ah yes, we have a misunderstanding hear, I was referring to the over-wing design, I don't think that's a good idea when it comes to re-entry because you'll get a trapped gas layer around the fuselage due to the speed, worsened by the resulting pressure differential, so you'll be burning around the body as well => more surface area subjected to the extremes of heat.

As for the inlets:

http://www.avatar-forums.com/images/imported/2010/11/451.jpg
Located right bellow the leading edge of the wing. They do puzzle me to be honest.

[MarkD]

Hmm, well perhaps a wind tunnel model should be built. There is that 1/288 scale model of the Valkyrie already built. Someone could test it on how the air flows over the model. That's the only solution I can see regarding how it would look in flight.

[Unil Makto]

Hmm, well perhaps a wind tunnel model should be built. There is that 1/288 scale model of the Valkyrie already built. Someone could test it on how the air flows over the model. That's the only solution I can see regarding how it would look in flight.
You wouldn't happen to have any sim packages?

[MarkD]

None. I saw on Mythbusters how to build your own small wind tunnel. All you need is something to put the model on, a fan, and something to direct the air flow.

[MaverickSawyer]

Hate to drag up a long-abandoned post, but I happen to have the answers you are looking for.
Orbital Entry: If you look at the layout of the ISV, the Whipple Shield is in the "front" when travelling, and the engines at the "back", where they face "forward". When you want to slow down, you simply fire your engines. Not turning required.
Orbital Orientation: The biggest challenge is going to be gravity gradients. Place a long object like the ISV in an orbit, and it will want to rotate to face more or less straight up and down, relative to the surface below. Gyros and thrusters would be essential to maintaining orientation, especially during docking operations with the shuttles.
Orbit Type: Probably a low altitude orbit, to enable a low-energy climb by the shuttles. Also, the orbit has to be inclined to fly over the Hells Gate vicinity at least once per day. Probable orientation is a few degrees above the latitude of HG.
Escape Velocity: This is where complex things need to happen in a precise sequence. Step one: point the engines so that the ISV will be pulled along and speed up. I would use the Gravity gradient to help get the rotation started and stopped, and use the attitude control system to assist with the precision alignment. Step two: acheive Pandora's escape velocity. Easy enough: just light the engines and go. Ensuring proper trajectory for system departure is likely assisted by gravity slingshots by the primary planet Polyphemus and the other moons.