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FAQ
How big would BOSS be?
The simple answer is as big as you can make it.
Realistically, our current design calls for a 70m x 70m sheet
of clear polyimide 8 microns thick, supported by inflatable or
otherwise deployable booms. Total mass (including
communications gear, attitude control, ion-engine propulsion
system, ...) ~ 300kg. Add to that an equal mass of propellant,
for a total mass of about 600 kg.
Where does the BOSS satellite get deployed?
There are two configurations under active consideration:
- Space-Space Configuration
- In the space-space configuration, BOSS is placed in
orbit in conjunction with a
space telescope. The space telescope might be at or near
theL2
or 2nd Lagrangian point of the Earth-Sun orbit. BOSS
would be flown around the space telescopes at distances of up
to 200,000 km. L2 is a point in space, 1.5 million km past
the Earth along a direct line from the Sun to the Earth. At
this location the gravitational pull of the earth and sun
combine in precisely the right a way so that a satellite
placed there will orbit the sun with a period of exactly one
year. The Next
Generation Space Telescope, the planned successor to the
Hubble Space Telescope, will probably be placed in orbit
around L2 in the middle of the next decade.
- Space-Ground Configuration
- In the space-ground configuration, BOSS is placed in a
highly elliptic orbit around the
earth. The apogee of the orbit (the furthest the satellite
travels from the center of the Earth) is about 200,000 km;
the perigee of the orbit (the closest the satellite gets to
the center of the Earth) is about 15,000 km. The orbit is
designed such that at apogee the velocity of the satellite is
precisely the same as the velocity of a telescope on the
surface of the earth. (This means that in practice you must
adjust the orbit for the particular telescope with which you
are observing.) This allows for much longer "hang
times" (up to 1500 seconds) than one gets with a natural
satellite such as the moon in a nearly circular orbit,
although less than in the space-space configuration.
How do you steer the BOSS?
Using a combination of
ion engines and solar sailing. Ion engines (a.k.a. Electric
propulsion) utilize electric fields to accelerate ions to
very high velocities. These high velocity ions make ideal
propellants, especially for low mass satellites such as
BOSS. Because BOSS is so large and light, it also makes an
ideal solar sail. Light from the sun is reflected or absorbed
by BOSS, transferring momentum to the satellite. By appropriate
adjusting the attitude, reflectivity, and/or center of mass of
the BOSS one can steer the satellite to the desired location on
the sky.
How well does BOSS work?
The answer to this
question depends very much on exactly what you want BOSS to
do. Most importantly it depends on the telescope(s) with which
it is associated, how far away BOSS is from the telescope, the
wavelength at which you observe, the duration of the
occultations, the accuracy in position and velocity control
that one achieves, etc. But, one good figure of merit is that a
70m x 70m BOSS at 100,000 km blocks all but 0.0015% of the
light from an occulted star. To start with we will show
some images of our solar system at different distances
away. Here we are using a 70m x 70m BOSS 100,000 km from an 8-m
space telescope (like NGST). The images produced here assume a
3000 second integration time. More details can be found in our
ApJ Paper [Postscript,pdf] we have submitted.
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