Posted on 04/12/2009 12:15:48 PM PDT by 1believer
Actually, it sounds very realistic!
To begin with, before I read on, I initially thought your entry would be blunt face-on, rather like the U.S. re-entry capsules. That of course generates the highest temperatures but gives the quickest re-entry. The disadvantage is the need for an insulating and/or ablative heat shield for which, today, is rather delicate otherwise and definitely not a good idea for anything beyond relatively short orbital missions. The problem of an ablative shield is obvious.
(BTW, my last project at NASA was a realtime data analysis & reduction program for a vibrational structural analysis of a sample prototype Space Shuttle heat tile. For all it paid poorly -I was a student then- that was one of most exciting jobs I ever had.)
So you're going in edge-on and rotating. First off, that seems like you might have major control problems maintaining that orientation -- once you're anything but dead-on there ought to be major forces pushing the craft into blunt-on orientation. My forgotten physics does not inform me what the effect of (presumably) rapid rotation does to those forces, but I think of tops and think of the shift to blunt-on involving a horrendous spiral rotation into the blunt-on position. I would NOT want to aboard in any container whose relationship to me was tied to ship orientation!
Next, I'm not sure you're going to get a whole lot of cooling effect by rotating. It's not like the craft is exposed to cool breezes on the backside -- my limited understanding (of capsule entry) is that you have something of a bubble of coolER air behind, surrounded by the superheated air from the foreward edge.
On the other hand, if you come in edge-on, you're presenting quite a bit less drag, which means lower temperatures overall though a MUCH longer (both time and space) re-entry trajectory.
And you fly on airplanes.
You're a braver man than I am, Gunga Din.
Your observations and concerns are accurate and appropriate.
What you’re missing is that you’re looking at atmospheric entry from orbital speed, which I initially seemed to imply.
Only later did I introduce the concept of the Rotavator, which lowers the craft into the atmosphere at less than orbital re-entry speed.
All we need is to control the effects of the motion through atmosphere as if it were falling from height.
For this purpose, the rotation of the outer hull rim allows any heat developed to be spread evenly through radiative emitting, (black body radiation).
This is as a paean to the shuttle ablative tiles. Rather than let only some front facing edge absorb the brunt of ablative damage, the forces are spread over a larger area.
As for the dynamics, it’s true that gyroscopic forces could be difficult to control, except that nothing is trying to twist the incoming spacecraft off axis. The rotation simply adds stability.
Additionally, the mass of the rotating surface is small in comparison to the overall mass of the ship. It will be stable. All will be well.
Trust your pilot.
I mean, fer cryin' out loud! It's a freakin' Flying Saucer!
Ya gotta have things rotating!
Actually, that was my primary concern. Shifting from being neutral in a solar-centric frame to being "neutral" in a planet-centric frame involves a huge transfer of energy. Whether you do it up front in a "RotOvator" or by re-entry doesn't change the situation -- you enter both with the same energy vector and depart with the same energy vector; the only question is how you got from the first to the second.
For this purpose, the rotation of the outer hull rim allows any heat developed to be spread evenly through radiative emitting, (black body radiation).
My concern is that the energic input (heat) in the braking phase is not likely to be met by the backside (thermal) radiative element. The skin could still heat up to aand beyond the failure point.
I'm not familiar with your terms of description. However, it may help to visualize your car tire rotating along the highway, as the Rotavator is rotating along in its orbit.
A point at the top of the tire is moving at twice the speed of the vehicle, but as the rotation brings it around to the bottom, its speed relative to the highway drops to zero.
In the same way, the flying saucer will be attached to the Rotavator's tentacular arm, and will be subject to acceleration outward (downward) at the bottom of the rotation.
Release from the Rotavator tip will put the ship into free fall and atmospheric entry. It is at this stage that it encounters friction from the air. It adopts the edge-on entry configuration and prepares to slow its speed through aerodynamic braking. Exactly where in this descent the ship changes over to its maximum resistance, its flare, will be determined by analysis and testing for stress loading.
Eventually, the flying saucer will have transitioned from frisbee to parachute aspect, and its aerodynamic braking will be at a maximum.
It may help you to envision this process operating in reverse, when a shuttle comes up from the atmosphere to meet the tentacle end of the Rotavator. It will fly almost straight up out of the atmosphere and be snagged by the Rotavator tentacle tip.
Should the attempted grab miss its connection, the shuttle would be constrained to fall back into atmosphere, orient for re-entry, and return to its origin.
Original entry from a Rotavator is no different from a missed capture.
Back to the falling Flying Saucer.
To further slow descent, the counter-rotating rings, equivalent to helicopter rotors, will provide stability and downward thrust until the appropriate altitude is reached. Then under a stable altitude profile, the ship begins expanding.
Note that the entire entry could have been accomplished with a flaring aspect, unless that would have exceeded the deceleration profile for the vessel.
This type of entry allows the somewhat safer method of deceleration of a de-orbiting burn using the on-board shuttle thrusters to counterthrust, even from orbital speed, and then transition to aerobraking when possible.
Recall that the scramble, or abort to orbit, will require full thrust from the shuttle thrusters until the ship can be rejoined with the Rotavator, which has gone on its way around the planet. This type of safety abort is probably more dangerous than anything that would happen from continuing the mission.
The Flying Saucer, with Nuclear Shuttles, is capable of entering Venus atmosphere from orbit, by doing an extensive de-orbit burn and then an atmospheric entry. The problem arises from needing to have enough reaction fuel aboard. The preferred volatiles to carry are Oxygen and Nitrogen, and it would be very frustrating to have to vent them unnecessarily.
(I think I have it all put together. Check me, will you?)
It's good that you are visualizing the procedure and anticipating possible problems.
There really are some advantages to this design, and to using a flying saucer platform. In this instance, it is atmospheric friction that is causing heating, and the rotating hull surface is backed by counter-rotating rings for atmospheric thrust.
If the heat generated by entry friction cannot be dissipated by radiation alone, the air-movement rings will be pushing the hot air around and using it for deceleration thrust, as well as providing cooling for the hull ablative ring.
If that concerns you I'd suggest you skip the maiden launch of the Flying Saucer into Venus atmosphere. Wait for a shuttle connection instead.
Just got home from work.
Yes, I needed to be defibrillated due to no coffee, undead were driving, and I got swarmed by angry crickets while the bunny sat and glared at me darkly.
And that was the harmless stuff.
LOL. It’s Monday all right. Class coming up in 35 minutes — need to prepare. Or not.
My husband got a book out of the bookcase last night and found a cricket sitting on it. I guess a bunny wouldn’t help, but the dragons aren’t much use, either.
Howdy, all.
I’m heading for the Post Orifice soon, but wanted to just let y’all know I survived Mother’s Day!
Two of my three favorite people called, so I went to bed with a happy face! *snirk*
Dragon one: “Cricket? Whassat?”
Dragon two: “I dunno, let’s go chase the cats.”
I had all of my nieces and nephews outside.
One of them can outshriek a low flying airplane.
Guess what they did outside my window while I tried to sleep?
My mother-in-law called yesterday. It was nice to talk to her - that is, listen to her, because she talks too fast for anyone else to talk ;-).
I just returned from the P.O. ($.02 stamps) and getting my hair cut. 70s and rainy today, feels very good!
Don’t tell me...let me guess: outshrieking the airplanes.
;o]
My haircut will have to wait till my birthday.
I’m so glad for sunshine!!!
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