
Spacecraft Power (2016) - daredave
https://www.jpl.nasa.gov/video/details.php?id=1443
======
struppi
Just a side note:

    
    
        This kind of research could help us on Earth, too. For example, 
        some of the heat that gets wasted when you drive your car could 
        be reused and put back into the car to charge the battery 
        or power electronics.
    

I once worked for a company on software that was, among other things, used to
optimize the fuel efficiency of cars. There was some talk about how using
Thermoelectric Generators (TEGs) to recover the waste heat form the exhaust
pipe would be really cool - But that those TEGs were too heavy, too
inefficient and too expensive to make any sense in a car.

So maybe, this is the breakthrough that was needed. If this technology could
recover a few KW from the waste heat, this might greatly improve the fuel
efficiency of cars. Or it is just some marketing talk, like, "Look, what we
are researching here might be useful to YOU too"...

Can somebody comment on that?

~~~
TeMPOraL
> _Or it is just some marketing talk, like, "Look, what we are researching
> here might be useful to YOU too"..._

A common question raised by many people is why spend money on space
exploration when there are problems to be solved here, on Earth[0]? So NASA
and many others try to address it by pointing out just how much of their work
end up being used to improve life of everyone down here, on Earth. NASA in
particular seems to have boosted their marketing budget recently; something I
wish ESA would do too, to get more recognition and public support.

Also, this is a perfect moment to link to the classic:
[http://wtfnasa.com/](http://wtfnasa.com/) :).

\--

[0] - Besides space exploration being _fucking awesome_ , which for some
reason isn't widely recognized the axiom it is.

~~~
TranceMan
>Besides space exploration being fucking awesome

I don't see how space exploration is feeding the starving. It would be fucking
awesome if we solved that. It maybe a strawman - couldn't these millions be
spent on Earth? Instead we have commercial TV asking us to donate to solve
problems on Earth.

~~~
TeMPOraL
Yes, it would be. Being awesome for some (like myself) is obviously not an
argument in itself; I added it as a bit of humour :).

Regarding your very good question - it has been asked before. I'll direct you
to the classic:

 _In 1970, a Zambia-based nun named Sister Mary Jucunda wrote to Dr. Ernst
Stuhlinger, then-associate director of science at NASA 's Marshall Space
Flight Center, in response to his ongoing research into a piloted mission to
Mars. Specifically, she asked how he could suggest spending billions of
dollars on such a project at a time when so many children were starving on
Earth._

 _Stuhlinger soon sent the following letter of explanation to Sister Jucunda,
along with a copy of "Earthrise," the iconic photograph of Earth taken in 1968
by astronaut William Anders, from the Moon (also embedded in the transcript).
His thoughtful reply was later published by NASA, and titled, "Why Explore
Space?"_

The response is to be read here: [http://www.lettersofnote.com/2012/08/why-
explore-space.html](http://www.lettersofnote.com/2012/08/why-explore-
space.html).

~~~
TranceMan
Thanks, I have read that. It seems to have a premise that we can only feed all
the people on Earth from space. Is farming really dead?

When will this promise be delivered? It's been 40 years and I can imagine
Billions spent. Are people still starving?.

~~~
the8472
> Is farming really dead?

No, there's plenty of research to make agriculture (industrial and subsistence
farming) more efficient. But it's not trivial getting it into the hands and
heads of people since you can only do that locally.

> It seems to have a premise that we can only feed all the people on Earth
> from space.

No. Nasa and noaa are _contributing_ some parts to a larger machinery. It is
not the sole purpose of space missions, but it is a synergetic effect. You
need weather forecasts to optimize farming, satellites help with that. GPS
helps with international trade which in small part also covers shipping of
fertilizer or pesticides to countries.

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smoyer
"But as we improve radioisotope power systems, they can go for longer and
longer--powered by heat, even in the cold expanse of space."

Since the amount of electricity generated is related to the temperature
difference, the fact that space is cold actually helps quite a bit.

~~~
devb
Space is extremely cold, but only offers radiative heat transfer, which is not
nearly as efficient as convective transfer. It's hard to dump heat into a
vacuum.

------
the8472
Nasa was also researching a stirling engine based RTG (as opposed to
thermoelectric), but lack of funding has put that mostly on ice

[https://en.wikipedia.org/wiki/Advanced_Stirling_radioisotope...](https://en.wikipedia.org/wiki/Advanced_Stirling_radioisotope_generator)

------
aphextron
Can this type of system be safely used in LEO?

Since the SpaceX launch recently I've been thinking about a system that would
negate the need for an expendable second stage. If you had an "orbital taxi"
sitting in LEO waiting to grab the payload from the first stage and boost it
up to GTO, you could make the entire system reusable. The "orbital taxi" would
have to be powered by some kind of nuclear reactor like this using VASIMIR
propulsion
([http://www.adastrarocket.com/aarc/VASIMR](http://www.adastrarocket.com/aarc/VASIMR)),
as solar panels wouldn't be sufficient.

I'm sure this isn't a new idea so I'm wondering if anyone knows of such a
design?

~~~
hwillis
At that point you start getting into "why not just build a space elevator?"
territory. If it's just trailing into LEO, the first stage doesn't even need
to make orbit to get to GTO. That makes recovery way easier as well as
increasing the payload massively.

A space elevator of that type is within current technology, and while the cost
is obviously higher than a "taxi", the benefits are as well. In answer to your
question you could just eat the cost problem and use a really big battery + a
large number of taxis, and accept that they will have slow recharges.

NB that there will be a complication with launch windows with both a taxi and
a space elevator. You have to be limited more closely to orbital times without
a second stage. My personal favorite is still an orbital loop- put a huge
superconducting filament in orbit around the earth, then hang tethers from
magnetic bearings. There is almost no tensile stress on the loop, so no need
for fancy carbon nanotubes- it just needs a sufficient superconductor and
enough mass to stay in a stable orbit.

The downsides are of course that the power requirements are staggering, the
cost of getting that mass to space is staggering (although much cheaper than a
space elevator), and if power fails the tethers fall down (safe but
inconvenient).

Edit: as for the RTG- the power, even with these improvements, is waaaaaaaaaay
too low. This is a 25% improvement, to RTGs which are in the hundreds of watts
and weight hundreds or thousands of kg. VASIMR systems use tens of kW. It also
is not possible to make many more RTGs, and certainly not very large ones-
they are remnants of cold war nuclear power-building. It is _immensely_
expensive to produce these isotopes. Each one is a work of international
diplomacy and bureaucratic art.

It would not be possible to make them hundreds or thousands of times larger,
which would be required to be comparable to rockets. Not to mention, these are
still filled with radioactive material.

------
degenerate
I've only seen about 3-5 of these "drawing hand" template videos and already
they seem tired/overused.

~~~
yalooze
To offer a different view, I've seen lots of them and I found this one very
informative. I think it did a great job of keeping the viewer focused, and
slowly building complexity by drip feeding new details as it went. Loved it.

