Re: rutans roton, again

Steve VanSickle (
Thu, 7 Jan 1999 10:22:32 -0600 (CST)

On Wed, 6 Jan 1999, Spike Jones wrote:


> this is the critical statement on the whole site. my task, before
> i start buying roton stock, is in determining exactly what the
> comment means. if it means an empty roton is 5% heavier than
> an empty atlas, while holding 24% more fuel by mass (the only
> logical interpretation of the statement) well, then im impressed.
> i grant that it is possible, since a kerosene tank is much smaller
> and lighter than a tank that could hold an equal mass of liquid
> hydrogen.

Atlas did not use liquid was Kerosene/Lox like the Roton is. Roton saves empty mass by widespread use of advanced composites instead of the stainless steel the Atlas body/tank was made of. And Roton stock is not available to the public (unless you have several hundred thousand you want to invest to make it worth their while to push it through the SEC). I think there may be an IPO after testing.

> next i must do the calcs. i have weights of the empty atlas, so
> from the info given, weight, size and specific thrust (i will assume
> they really did somehow figure out how to get 350 seconds vac isp
> out of kerosene and lox with a 400 psi chamber pressure) i can
> estimate (optimistically) drag coefficients and see if they really do
> have a chance of getting to orbit that way.

I thought they were running at higher pressure than that, but I could be wrong. Even at higher pressure and aerospike altitude compensation, it will be a tough goal. If 350 sec is an average for the whole flight, 9300 m/s delta-v (which is a good estimate including drag and gravity losses) the mass ratio is 15 or so. Even if the averaged specific impulse drops to 320, the mass ratio stays under 20.

> as for using an autogyro reentry system, i have gone even crazier
> trying to figure out how they could make that happen. every
> version of that i can imagine would be nowhere near handling
> the heat load of even a no-payload reentry. at best, i could imagine
> blades that would deploy very late in the reentry event, after going
> subsonic. this creates the need for a heatshield, which defeats most
> of the advantage of the autogyro system in the first place.

The rotor blades will deploy upward before reentry (like an umbrella blown inside-out) and stay in the lee of the shock way, minimizing heating. There, they will make the vehicle passively stable (so that loss of the reaction control system won't result in the vehicle losing control) but they won't be spun up for lift until the vehicle slows to sub-sonic. The heat sheild they are designing will be water transpiration cooled (think of it as an ablative heat shield, where the ablative material is water and it's replaced every flight). They expect to use rotors for hypersonic lift on later vehicles (both take-off and re-entry) but they now expect to have to actively cool them. That is more risk than they want to take on for a first generation vehicle.

> on the other hand, the system could perhaps be made so simple and
> cheap it would not be so critical to recover anything.

Doubtful. True land that sucker, fuel it up, kick the tires and fly again reusability is the only way they will be able to take on the big boys.

> the whole exercise gives one a new respect for how deep a gravity
> well we are in down here. spike

Actually, I've been growing more and more appalled at how the cost and difficulty of spaceflight has been over stated over the decades. Only a government monopoly would think a disposable spacecraft reasonable (for other than the most basic test purposes). But once NASA established the status-quo, no one was able to buck it until now. I think Rotary will pull it off, if they have the financial ability to weather the loss of one or two vehicles during testing. A lot of "rocket scientists" will have a lot of explaining to do.

steve van sickle