If (the big IF) the propellant is safe and stable and yields good enough
performance I can see advantages from it providing (as John mentioned) you
don't have to modify the F15. You get some of the advantage of avoiding sea
level atmosphere ops allowing good nozzle and mass ratio optimisation for all
your rocket staging (allowing propulsion system simplification) and you get a
pretty reliable 1st stage and probably a reliable 1st-2nd stage transition
given that it's similar to what the air force do for their primary ops. If the
numbers say the weights are within the envelope (remembering we're not
operating in a combat environment here) then that's a big start.
Troy
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Monroe L. King Jr.
Sent: Thursday, 7 January 2016 9:08 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Pilot, ALASA, and cubesat launch (was Re: some interesting
developments)
I do buy that.
I don't buy however that the F15/Monopropellant is any better.
IF a fighter aircraft has to carry that much weight it's too dangerous and you
loose the properties that make a fighter worth using.
Wither Pilot worked or not the principal is sound of air launching from a
fighter
You just cant screw it all up with a big payload.
-------- Original Message --------
Subject: [AR] Pilot, ALASA, and cubesat launch (was Re: some
interesting
developments)
From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
Date: Wed, January 06, 2016 1:11 pm
To: Arocket List <arocket@xxxxxxxxxxxxx>
On Tue, 5 Jan 2016, Monroe L. King Jr. wrote:
"(I still want to know how a rocket that was spin-stabilized in a
70deg climb, then magically tipped over to near-horizontal at 80km..."
...The altitude of the rocket was not great enough for the spin to
maintain attitude because of drag which allowed the rocket to turn
enough to reach the right angle for third stage ignition.
I'm still a bit skeptical -- a trajectory that steep has most of the
curvature right at the top, with velocity quite low and air very thin
-- but I'm not saying outright that it wouldn't work, only that it
sounds rather marginal and I wouldn't be surprised if there was a problem
there.
(And one thing that's clear from the accounts of Project Pilot is that
it was an extreme rush job and some experienced people had doubts
about it.)
So what your saying really is it's not cost effective to build a 3Kg
launcher for cubesat payloads.
No, I didn't comment one way or the other on that. What I said was,
that wasn't what ALASA was trying to do. They evidently thought that
the US military would be a lot more interested in 30-45kg, which is
undoubtedly true. (ALASA's nominal payload was 100lb into very low
LEO; payload to a more practical orbit would be somewhat less.)
However, since you ask...
Maintaining a Mig 29 and using an expendable launcher that weighs in
the 2000lb range for commercial use to put cubesats into orbit on a
regular basis is not a viable business plan.
...That is what your trying to say correct?
Indeed, I rather suspect that such a concept is not viable.
Maintaining a hot jet fighter is expensive; Mitch's comment on a
commercial ALASA was that you'd need really high launch volume to
justify a privately-owned F-15. And when looking at the cubesat
market, you have to remember that 90%+ of it is poverty-stricken
student projects that *want* to fly as cheap or free secondary payloads.
When you start trying to build nanosats with serious payloads and
solid engineering and paying customers, you discover rather quickly
that you want a somewhat larger volume than a 3U cubesat, and
preferably a less elongated one too. If you're trying to accommodate
paying customers, not just today's but also tomorrow's, I'd suggest looking
at the "12U cubesat"
specs of outfits like <http://www.planetarysystemscorp.com/> (there is
no industry-wide standard beyond 3U). That's circa 22x22x35cm, 20kg+
(*not*
20x20x30 and 12kg, as you might think from that misleading "12" number
-- even the 3U cubesat standard actually allows more than 3.0kg).
And don't forget that cubesats are built to fly in deployers that can
weigh as much as they do. You can undoubtedly reduce that some, but
not to zero -- it's not a matter of just a little mounting ring, not
if you want to launch standard cubesats. (And for that matter, if you
read the specs from people who build things like those rings, you find
that their small ones are noticeable chunks of hardware with
nontrivial mass -- they don't scale down linearly.)
In short, I think a realistic commercial "cubesat" launcher *should*
be aiming at something close to ALASA's payload. I don't think you're
going to make it pay at 3kg.
Henry
