[extropy-chat] Pluto New Horizons launch -getting ready

[spike]

________________________________________
From: extropy-chat-bounces at lists.extropy.org
[mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of Robert Bradbury
Sent: Monday, February 13, 2006 12:46 PM
To: ExI chat list
Subject: Re: [extropy-chat] Pluto New Horizons launch -getting ready


Just to continue on this thread.  According to [1], New Horizons will be
going ~50,370 km/h when it passes by Pluto.  Compare that with the Stardust
sample return capsule which hit the Earth's atmosphere at ~ 46,660 km/h --
that isn't *that* big a difference.  Now I realize that Pluto doesn't have
much of an atmosphere one can use to slow one down but there ought to be
ways (as I mentioned previously) to compensate. 

Robert

1. http://www.aerospaceweb.org/question/spacecraft/q0260.shtml



Assuming no atmosphere on which to use aerobraking, and the
gravity field relatively small, we would need to come up with
a delta V of about 14 km per second.  A typical rocket motor
capable of being carried out to Pluto (non cryogenic fuels)
might be able to make a specific impulse of about 3000 N-sec/kg
(hydrazine motor), so assuming you are only injecting into
Plutonic orbit you still need about 12 km/sec delta V, so you need
about four times 3000 to get to there, so e^4, so your mass fraction
of fuel in that bird is about about 98 percent fuel by
mass when it starts its deceleration burn.  The 2% not-fuel
must include the weight of the tanks, the motor etc.  This
isn't necessarily flat out impossible, but it sure looks
flat out impractical to me.  I see why the mission designers
decided to zing on past while taking pictures, then take their
time in sending the info back home.

Robert we need you to invent nanotech so that we can blast out
there with payloads of only a few milligrams.  That solves so
many of our stubborn propulsion problems.  {8-]

spike




spike