[AR] Re: $1M prize for a student rocket reaching 100 km
- From: Ben Brockert <wikkit@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 15 Sep 2018 15:59:26 -0700
(old thread, but I think it's important)
crogers168 said:
It just would have been a lot better to have an altitude for the prize of 100K
ft or 200K ft. How high has an amateur or university liquid rocket flown? A
100K ft prize, with a lower prize amount, would have had multiple competitors.
Per an ARocket thread from some years ago, designing a prize like the CATS
Prize, the XPrize or the Lunar XPrize, is a difficult endeavor.
With the lower altitude you could use a max possible range/max probable range
approach, and avoided needing an FTS.
The prize rules state that the team needs to get a Class 3 waiver for the
rocket, which means FAA approval, and FAA approval for the FTS.
If by "FTS" you mean the classical sense of an independent
radio-actuated flight termination system, there is no need for that
kind of FTS on a 100km Class 3 amateur rocket, guided or not.
The team would need to get a class 3 waiver because a class 2 rocket
can't make 100km outside fanciful spreadsheets, and asking student
teams to get a launch license (for a >200,000 lbf*s stage) is asking
too much. For scale, Armadillo's Stiga was about 200,000 lbf*s on the
nose; it seems well beyond the size most university projects could
attempt. It would almost certainly cost more than $1M to build and
test and get such a rocket to 100km if that task required any
learning.
Masten, Armadillo, EXOS, and other suborbital rockets don't have FTS.
They typically do have a variety of other aborts, including
Instantaneous Impact Point (IIP), but it doesn't have to be an
independent system. Armadillo demonstrated successful IIP cutoffs on a
bunch of occasions. Regardless of the trajectory and FAA implications
you want that system anyway, to restrict your range for Ec/insurance
reasons, and because nothing good can come from continuing to run
propulsion while your rocket is tumbling or far off axis or whatever.
Now, an aside about FTS more generally:
By law you are not even required to have independent FTS for an
orbital rocket. SpaceX is flying AFTS, which is a separate system but
doesn't have a radio terminate link. From conversations with FAA
people I'm convinced that they could be convinced that even that is
unnecessary. A modern rocket with MEMS IMU and GPS is fundamentally
different than an old-school rocket with high grade IMU and no GPS.
The modern rocket can't fly a trajectory without the GPS, which means
it can't fly without knowing where it is, which means it can't fly to
the wrong place without knowing that it's in the wrong place. The
point of classic FTS is that rockets with purely inertial guidance are
perfectly happy to fly to the wrong place while not knowing it, so the
ground has to keep track and tell them to stop flying if they go
wrong.
It's likely that the AFTS is the system optimum for low flight rates
or large rockets; it costs you another GPS systems and a computer, but
means that the FAA only has to be interested in that tiny codebase and
not all of your flight software codebase. For a low cost expendable or
a high performance smaller reusable I think the trade likely goes to
having the abort system as a core part of the normal control system.
Ben
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