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NASA just launched 8 satellites from a rocket dropped from a plane at 40,000ft

theregister.co.uk

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Re: NASA just launched 8 satellites from a rocket dropped from a plane at 40,000ft

#41

Post by Analemma_ »

peteretep wrote: post #39

This is probably a tremendously dumb question, but what are the major impediments to literally sticking a big freaking balloon to the top of a rocket and floating it up much of the way?

It wouldn't save you nearly as much fuel as you'd think. The majority of the delta-V (fuel) to get something into orbit is for pushing it sideways, not pushing it up - you need about 8 km/s of sideways speed to get into even a low orbit, and that's where the the fuel is going. When you see balloons lifting cameras (or people) out of the atmosphere, they're going to space, but not to orbit - they fall straight back to Earth as soon as the rope is cut, even though they might be at the same altitude as the ISS which does not fall.

xkcd had a helpful explanation about the vertical/horizontal mistake that is often made when thinking about space travel: https://what-if.xkcd.com/58/

Re: NASA just launched 8 satellites from a rocket dropped from a plane at 40,000ft

#42

Post by blater »

peteretep wrote: post #39

This is probably a tremendously dumb question, but what are the major impediments to literally sticking a big freaking balloon to the top of a rocket and floating it up much of the way?

Why bother with the rocket? It sounds mad, but you can actually just send the balloon. to orbit... http://www.jpaerospace.com/atohandout.pdf

Re: NASA just launched 8 satellites from a rocket dropped from a plane at 40,000ft

#43

Post by phamilton »

planteen wrote: post #37
wrigby wrote: post #30

Earlier quoted context omitted.

IIRC, star trackers are used as both a position and an attitude reference. GPS gives you only position (though more sophisticated systems can be used to determine attitude). While a GPS outage is a minor inconvenience for most of us, it could be pretty catastrophic for spacecraft if they didn't have another position reference. EDIT: See below - I was off; they're just attitude, not position

Star trackers are usually just used for attitude, not position. I've heard of research to use them in conjunction with a camera pointed at Earth to resolve coastlines to get position, but it's very theoretical at this point AFAIK.

For those of us just watching, what is attitude? At first I though spellcheck might have corrected it from altitude, but 3 times among 2 differently people I see attitude.

Re: NASA just launched 8 satellites from a rocket dropped from a plane at 40,000ft

#44

Post by nickik »

astrodust wrote: post #19
ygra wrote: post #16

Earlier quoted context omitted.

That'd require a rather huge balloon. Rockets are quite heavy. Pegasus XL has a mass of over 18 Mg, for payload mass of just over 400 kg. Not sure how this relates to SpaceX' drone ship landings. Falcon 9 couldn't launch from the air, as cryogenic fuels mean you have to launch rather soon after fueling. Furthermore fuel is cheap (compared to the rocket), and their mode of operation seems to work rather well (despite…

The thing about balloons is they're relatively cheap, and the stuff you put in them isn't expensive either. If you want to flirt with danger, hydrogen filled is one way to do it. The drone part is mostly to do with automation, as a terrestrial platform allows a lot of hands-on work to prep the rocket for launch. A high-altitude platform would have to be automated. Plus the way rocket physics work is the less fuel you…

There is a reason basically nobody ever uses a balloon, it just does not make sense. It does get you far to little for not enough. You don't save that much energy and you have way harder time starting.

You can't do deep cryo fuels and you can't do static fires in lunch conditions.

Re: NASA just launched 8 satellites from a rocket dropped from a plane at 40,000ft

#45

Post by andrewflnr »

phamilton wrote: post #43
planteen wrote: post #37

Earlier quoted context omitted.

Star trackers are usually just used for attitude, not position. I've heard of research to use them in conjunction with a camera pointed at Earth to resolve coastlines to get position, but it's very theoretical at this point AFAIK.

For those of us just watching, what is attitude? At first I though spellcheck might have corrected it from altitude, but 3 times among 2 differently people I see attitude.

It's orientation, AFAIK, what direction it's facing.

Re: NASA just launched 8 satellites from a rocket dropped from a plane at 40,000ft

#46

Post by nickik »

sargun wrote: post #22

Orbital ATK has been building and launching the Pegasus XL ( https://www.orbitalatk.com/flight-systems/space-launch-vehic... ) for a bit now. It is an extremely cheap platform that is launched from an airplane. What's neat is the User Manual is available online: https://www.orbitalatk.com/flight-systems/space-launch-vehic... [pdf]

How is it extremely cheap? It can almost not compete now and it has very little option of re-usability. Everybody else is pushing for reusable systems, SpaceX is almost there.

If they could get a extremely high lunch rate the might be able to do it at a good price, but that will be hard.

Re: NASA just launched 8 satellites from a rocket dropped from a plane at 40,000ft

#47

Post by Retric »

ucaetano wrote: post #7

Lifting a rocket that high before firing it carries another benefit besides the (small) altitude gain and lower fuel requirements due to drag: Max Q, the maximum dynamic pressure that has to be sustained by the rocket usually happens at a lower altitude than that (depending on the mission). This means your rocket has to sustain a far lower structural load, making it safer and lighter.

The altitude gain is significantly less important than the horizontal velocity. An aircraft can easily launch from the equator and add 650+MPH.

Re: NASA just launched 8 satellites from a rocket dropped from a plane at 40,000ft

#48

Post by andrewflnr »

blater wrote: post #42
peteretep wrote: post #39

This is probably a tremendously dumb question, but what are the major impediments to literally sticking a big freaking balloon to the top of a rocket and floating it up much of the way?

Why bother with the rocket? It sounds mad, but you can actually just send the balloon. to orbit... http://www.jpaerospace.com/atohandout.pdf

Well, with some help from "hybrid electric/chemical propulsion". Also, hydrogen. Yikes.

Re: NASA just launched 8 satellites from a rocket dropped from a plane at 40,000ft

#49

Post by greglindahl »

Retric wrote: post #47
ucaetano wrote: post #7

Lifting a rocket that high before firing it carries another benefit besides the (small) altitude gain and lower fuel requirements due to drag: Max Q, the maximum dynamic pressure that has to be sustained by the rocket usually happens at a lower altitude than that (depending on the mission). This means your rocket has to sustain a far lower structural load, making it safer and lighter.

The altitude gain is significantly less important than the horizontal velocity. An aircraft can easily launch from the equator and add 650+MPH.

Note that this launch wasn't from the equator, because this constellation needs to overfly hurricanes.

It's fairly uncommon for LEO satellites to want to be at the equator. GEO, extremely common.

Re: NASA just launched 8 satellites from a rocket dropped from a plane at 40,000ft

#50

Post by bootloop »

devnonymous wrote: post #17
bootloop wrote: post #6

Earlier quoted context omitted.

Great! You didn't fuck it up than right? Or does it take some time to tell? I guess we will see soon. I will come back to you and this comment if they go down!

Yeah, we'll downvote the comment, that'll serve 'em right! :-)

I thought its funny... People are too serious. At first it even got some upvotes.
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