Unfortunately, at that end of the size range, a 4 kg payload to orbit
drops to zero long before you've scaled vehicle mass down by a factor of 4.
The main thing is, drag scales down slower than mass does. There are
also likely minimum-gauge factor problems that will start increasing
subsystem masses as a fraction of the whole as overall mass is reduced.
Both of these factors shave away payload fraction *as a percentage of
the overall mass* as you reduce overall mass. Payload fraction hits
zero long before you get down to 650 kg overall.
Dig into the actual numbers and I expect you'd find ss-520's designers
were already acutely aware of both those factors, and already sized
their vehicle's 2600 kg quite close to that zero-payload threshold for
their mix of technologies.
Henry V
On 2/18/2018 8:38 AM, Robert Clark wrote:
Trying to find the specs on the stages of the rocket such as thrust, Isp, mass ratio if anyone knows those. Some reports give the max payload to orbit as 4 kg. Then scaling it down to a 1 kg payload, perhaps a 650 kg rocket could launch a 1U cubesat to orbit. This would be in the size range a university team could produce of a APCP propellant rocket.
Bob Clark
On Sat, Feb 3, 2018 at 6:27 PM, Henry Spencer <hspencer@xxxxxxxxxxxxx <mailto:hspencer@xxxxxxxxxxxxx>> wrote:
On Sat, 3 Feb 2018, John Dom wrote:
3 kg highly eccentric orbit sat.
The highly elliptical orbit is unsurprising for the first launch of
an all-solid launcher. LEO orbit insertion is terribly sensitive to
small errors in the delta-V of the final stage, so if you want to be
sure the payload will stay up long enough to be verified, you use a
light payload that will give a rather high apogee -- that way you
don't care too much just *how* high the apogee is.
Especially so if orbit insertion is at low altitude and so the
perigee is going to be quite low. With perigee below 200km,
probably neither the payload nor the final stage will stay in orbit
very long -- air drag at perigee will bring down their apogees
quickly, particularly since small objects have high surface area per
unit mass.
As you can see SS-520 is by a wide margin the smallest (publicly
confirmed) rocket to reach orbit. A full 6.75 meters _shorter_
than Lambda-4S and only 2.6 tonnes at liftoff. It's tiny.
A quarter the mass of Lambda-4S and 3/4 the length of Black Arrow
(the former record holders in those categories, discounting the
faint possibility that Project Pilot reached orbit) is definitely
impressive.
Its only payload was a single 3U cubesat. If you want to know
what a minimal cubesat launcher design might look like, this is it.
However, if you want to know what a commercially successful minimal
cubesat launcher might look like, this probably isn't it. :-) At
the very least, they need to get the perigee up some. Precise
control of apogee (which almost certainly means a liquid trim stage
a la Electron), and a 12U or at least 6U payload, would also help.
Henry