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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

#21

Post by outworlder »

astrodust wrote: post #2

Given how SpaceX has landed things on a drone ship, presumably they're considering launching from a rocket that's been lifted above the bulk of the atmosphere using a balloon of some sort. You'd probably save a ton of fuel if you could launch from 40 or even 100K feet.

Hint: if altitude were such a problem, why don't rockets go straight up to 80km or so, and only then thrust sideways?

Rockets clear the most dense portion of the atmosphere very quickly. Building up speed is what takes time (and fuel).

Of course, the exponential nature of the rocket equation means that you'd get to save a lot of fuel. You'd still have to lift a lot of rocket though. With a balloon so big that would put the ships from the original Independence Day movie to shame.

Maybe it would be worth it on Venus.

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

#22

Post by sargun »

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]

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

#23

Post by TallGuyShort »

RelaxBox wrote: post #3
astrodust wrote: post #2

Given how SpaceX has landed things on a drone ship, presumably they're considering launching from a rocket that's been lifted above the bulk of the atmosphere using a balloon of some sort. You'd probably save a ton of fuel if you could launch from 40 or even 100K feet.

Eh, not really. It's not getting to altitude that's expensive, it's speed. Orbit is blisteringly fast.

When you're dealing with LEO velocities, the difference between the speed of the aircraft they launched with (significantly <M1) and a drifting balloon is relatively negligible considering the benefit of start at the edge of the atmosphere inexpensively, I would think. Definitely a new technique that would have some hard problems, but not fundamentally infeasible, I would think.

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

#24

Post by comboy »

planteen wrote: post #5

I worked on the software for the star trackers in these. Glad to hear they have already made contact. :-)

I can't get my head around how this thing works. Apart from the direct GPS signal it's able to also receive the part of it that was reflected by the ocean? How does the reflected signal tell anything about the wind speed?

And btw what are star trackers used for? As a fallback for GPS?

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

#25

Post by [deleted] »

patall wrote: post #10
AdamTReineke wrote: post #4

Earlier quoted context omitted.

It's expensive to build up speed while fighting through the lower atmosphere. Density drops pretty fast[1], so you don't need to fight it with the rocket if the launch vehicle has already paid the cost. [1] https://upload.wikimedia.org/wikipedia/commons/d/de/Atmosphe...

Why aren't space ports then at higher altitudes but mostly at sea-level like cape canaveral? At the beginning the rocket flies comparably slow, so the lower atmosphere density is not that important, its the speed that is hard.

[deleted]

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

#26

Post by lobster_johnson »

planteen wrote: post #5

I worked on the software for the star trackers in these. Glad to hear they have already made contact. :-)

Can you tell us some more? What the software is, what language, what hardware they're based on, etc.?

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

#27

Post by Retric »

msandford wrote: post #14
patall wrote: post #10

Earlier quoted context omitted.

Why aren't space ports then at higher altitudes but mostly at sea-level like cape canaveral? At the beginning the rocket flies comparably slow, so the lower atmosphere density is not that important, its the speed that is hard.

Because there aren't any places in the US where you've got 20kft mountains right next to the ocean, on the east coast. The idea is that you launch over the ocean, near the equator so that you're getting the first ~1000mph for "free" since you're launching with the earth's rotation instead of against it. Next to the ocean is for range safety. If it's over the ocean and it blows up you don't rain down parts on populate…

No need for the east coast. Hawaii's highest point is 13,800 ft above sea level and much closer to the equator both significant advantages. The real advantage to Cape Canaveral is it was in the middle of nowhere with lot's of open land.

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

#28

Post by Symmetry »

astrodust wrote: post #8
RelaxBox wrote: post #3

Earlier quoted context omitted.

Eh, not really. It's not getting to altitude that's expensive, it's speed. Orbit is blisteringly fast.

It's a lot easier to get up to speed if you don't have to deal with cutting through a heavy chunk of atmosphere on the way up. Plus, rocket designs could vary, be less concerned about aerodynamics, if they were starting from a launch platform already in very thin air. A wider, shorter rocket might work better in thin air, for example, but that would be impractical launching from sea-level as is tradition.

With a wider, shorter rocket and lower pressure you could also use wider engine bells, for more efficient thrust.

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

#30

Post by wrigby »

comboy wrote: post #24
planteen wrote: post #5

I worked on the software for the star trackers in these. Glad to hear they have already made contact. :-)

I can't get my head around how this thing works. Apart from the direct GPS signal it's able to also receive the part of it that was reflected by the ocean? How does the reflected signal tell anything about the wind speed? And btw what are star trackers used for? As a fallback for GPS?

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

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