[ExI] De-Orbiting Gold

[Kelly Anderson]

On Tue, May 29, 2012 at 10:27 PM, spike <spike66 at att.net> wrote:
>
> ... On Behalf Of Kelly Anderson
> To: ExI chat list
> Subject: Re: [ExI] De-Orbiting Gold
>
> On Mon, May 21, 2012 at 4:48 PM, spike <spike66 at att.net> wrote:
>>>...> Thanks Kelly, I didn't explain that very well.  If we go for
>> aerobraking, we are talking about very shallow reentry angles.  That
>> means high uncertainty on the reentry path.  Small uncertainties in
>> atmospheric density mean large uncertainties in landing spot.
>
>>...Ok, that makes more sense. It seems to me that there are two ways to get
> down... One, which is what everything I am aware of is to fire the rocket
> straight ahead which slows your speed and you drop to earth...
>
> Ja.
>
>>...Another, which probably isn't used, is to fire the rocket straight up
> into space pushing you down but not slowing you...
>
> It isn't used because it doesn't work.  There are orbit sims available
> online.  If you find a good one, post the URL.  Playing with those
> demonstrates that if you fire your rocket straight up, you don't de-orbit,
> you just waste your fuel and get stuck in orbit.

Really, that's counter intuitive. I found plenty of planet simulators
but no satellite simulators that include atmosphere...

>>... I figure that with monkeys in the can, you want to be going as slow as
> possible, is that right?
>
> Ja, but it is a tradeoff, as you can find if you fiddle with those online
> orbit sims I mentioned above.  The shallow reentry angles require less delta
> V and produce lower peak decelerations, but introduce greater risk of
> skipping off the atmosphere and landing far from the recovery area.  This
> was the biggest danger during the Mercury days.  Gemini and Apollo could be
> steered to some extent by an offset CG, but the Mercury astronauts were spam
> in a can.  They didn't like that.

I would not like that either.

>  >...So would firing the rocket straight up give you more predictability,
> but a hotter entry?...
>
> No, it would probably result in no reentry at all.  It doesn't do what your
> intuition tells you it does.

Not at all, apparently.

>> >...upper atmosphere has waves and surges, like the ocean only thousands
> of times bigger.
>
>>...But would it not also be true that the bigger the variability, the less
> it would actually impact the orbiting object? If it's thinner, it seems that
> it would affect it less, and also be more exposed to solar wind effects,
> etc...
>
> What I mean is if you look at the atmospheric density in the critical areas
> where the most aerobraking is taking place, the variability is a lot higher
> than it is down here, where atmospheric density doesn't change all that
> much.  If you find a good reentry sim, it might have atmospheric density
> uncertainty programmed into it.

Ok, I think I am beginning to get it. It's "rocket science" after all... LOL

>>> If the reentry angle is too shallow, the reentry body (RB) might
>> actually start to go back out, a skip-off event a little like a flat
>> stone skipping off the surface of a lake.
>
>>...I've heard of that. I always figured you had to be going faster than
> orbital speed to get this effect...
>
> Orbital speed is quite sufficient to cause that effect if you come in at a
> shallow angle.  You need a competent control system to prevent it, for if
> you skip off just once, it introduces a great deal of uncertainty in the
> landing spot.

I can certainly see how that might be the case.

>>...And again, if you have a transponder in the object, does it matter, so
> long as it lands SOMEWHERE in the Pacific ocean?
>
> Sure but the Pacific Ocean is really big.  If your RB lands in international
> waters, then whoever gets there first owns that payload.

That's why you would need a very tricky transponder. And currently the
number of submarines that could get there is pretty low. I suppose you
could devise a mechanism to keep it 100 feet below the water... some
kind of buoyancy control.

> ...
>
>>...Ok, so there is a balance that has to be reached. What I'm asking is
> would that balance be significantly different if apes and fragile equipment
> were not on the list of concerns?
>
> I wouldn't think so.  The reentry path you would choose would likely be one
> that is survivable by apes.  Reasoning: to get the steeper reentry paths
> that result in higher peak Gs would require more delta V to start with,
> heavier structure to tolerate the higher heating and higher loads, you would
> need a sturdier heavier everything.
>
> Now to your point of using the gold itself as an ablative sacrificial heat
> shield, I don't see it.  You need to slow the thing down enough to not have
> it vaporize on impact I would think.

Ideally, you would use something other than gold... LOL What speed
would you have to be going to not vaporize on impact?

>
> That whole task is easy to underestimate.

Apparently.

> Consider that once you get your
> hunk of gold on board, you need to secure it such that the CG stays in one
> spot, you need a thruster system, tanks to hold the fuel, you need actuators
> to steer the nozzle, you need a control system to tell the actuators what to
> do, you need a gyro of some sort to stabilize the thing, or failing that
> some kind of really good thrusters to try to keep it all balanced, you need
> an inertial reference system so you know where to point the reentry thrust
> nozzle.  It would be possible, but it wouldn't be easy, and all that stuff
> would be heavy and costly.

So how does Burt Rutan's reentry system with the feathers work?

> I will leave it at this: if it is feasible to reenter a hunk of gold from
> LEO, it has only been recently that it is worth doing, as the price of gold
> went crazy.

If enough gold started coming in from outer space, the price would
seem like it would drop. On the other hand, if there were more
available, industry might start using it for more things. It is a very
useful metal.

>>> ... all I have seen so far is a number
>> of approaches which will not work for known reasons or are very high risk.
>
>>...High risk? Really, what's the risk? I mean risking a big ball of gold is
> clearly a risk, but you would practice with copper or something to get it
> right, no?  Kelly
>
> The risk is you would spend all that money to get your reentry system into
> orbit, then any number of things might go wrong and you don't get your hunk
> of gold back.  Space flight is still hard, even fifty years into it.  It is
> still an unforgiving game, still expensive as all get out and still no
> economies of scale.  You wouldn’t practice on a hunk of copper, you would
> practice on a hunk of gold.  Reasoning: even if your copper reentry scheme
> worked, you wouldn't get back a hunk of gold to pay for building and
> launching your reentry system.

Point taken.

> At this point I am still inclined to think if you had a hunk of gold in
> orbit, you would make stuff out of it there, wire, reflectors and such.
> Gold has some advantages over other metals for that sort of thing.

Surely that would be the thing you would want to do with it, but so
far the space manufacturing sector seems to be the same as that in
Ohio under the Obama administration's tender care.

-Kelly