From: eder@hsvaic.boeing.com (Dani Eder)
Newsgroups: sci.space
Subject: Re: Saving an overweight SSTO....
Date: 19 Jan 93 16:42:21 GMT
Distribution: na
Organization: Boeing AI Center, Huntsville, AL

Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) writes:

>> Dani Eder writes:
>> If you are trying to deliver cargo (not necessarily people) at the lowest
>> cost per kg, then the solution is to fly the DC-1 sub-orbital (to about
>> 0.7 of orbital velocity) and kick out the payload with a solid kick
>> motor attached.  The numbers go like this:

>        Interesting idea.  Without a full orbital flight, the DC-1 will not
>be able to land at its launch site.  Any idea on how far downrange the DC-1
>would land, and whether this could be accomplished within the width of the
>continental USA?  If not, or a Florida launch is needed to get a 28.5 degree
>orbit, where in Africa would be a suitable landing site?  A quick look at a
>globe suggests launching from Hawaii would require landing somewhere the the
>northern half of south America. Return to the launch site would presumably be
>by another suborbital hop, although this unfortunately means that two
>refueling and launch sites are needed and two DC-1 flights are needed to put
>1 payload into orbit.

>        Drawings of the current concept for the DC-1 show a mid-body cargo
>bay 15x15x30 feet with a door to the side of the spacecraft.  Once out of the
>atmosphere and finished the boost phase, the door will have to be opened and
>the payload ejected and the door shut again before the DC-1 reenters.  This
>has to work flawlessly in a very constrained time period - reentering with
>the payload bay door still open would probably be disasterous.  Any estimate
>of the time available between the end of boost and the beginning of reentry?

According to one source I have (Design Data for Astronautics and 
Aeronautics, R. B. Morrison, ed, John Wiley&Sons, 1962), for
a cutoff velocity of 18,000 ft/s, altitude of 100 miles, and path
angle of 5 degrees above horizontal, the range to landing from
cutoff is about 1500 miles.  Assuming 3 g acceleration to get to
speed, the acceleration distance will be 300 miles, so the total
range is 1800 miles.  The payload launch hop would be near horizontal
so as to leave the solid motor lined up for a LEO insertion.  

On the return hop, you would go for maximum range with minimum
velocity.  This would have a cutoff path angle of about 37.5
degrees above horizontal, and requires a velocity of about
16,000 ft/s (0.62 orbit velocity).  The peak height reached on
the return trip would be 2,200 miles.

This method of return is sometimes referred to as 'blast-back', as
contrasted to 'flyback' discussed for some boosters.

Time of flight from cutoff to re-entry would be about 5 minutes.  Note
that commercial aircraft landing gear doors operate flawlessly 
better than 99,999 out of 100,000 (there would be lots of crashes
that we would hear about otherwise).  So I would get guys who
do landing gear doors to do the design.

Baja California at 28.5 Latitude to the Kennedy Space Center works
out to be the right distance.  Note that while you are making two
flights, the engines will be running only 1.3 times the SSTO run
time, and the total heat load for the re-entry system is 0.87 times
the SSTO heat load, and it is divided into two re-entries, so the
heat shield could be lighter weight, since it dissipates less heat
each re-entry.  So, on net, I would guess that the maintenance
load for two sub-orbital hops would be about the same as for
one full SSTO flight.  Note also that the sub-orbital trips
are very short (about 20 minutes), so your electrical power
supply would be smaller than for an orbital mission (1.5 hours
or more).

Dani Eder

-- 
Dani Eder/Meridian Investment Company/(205)464-2697(w)/232-7467(h)/
Rt.1, Box 188-2, Athens AL 35611/Location: 34deg 37' N 86deg 43' W +100m alt.