scaling laws for satellites and probes?

dave and hank patterson wrote:
From my rather small knowledge of deep space probes, it strikes me
that they all seem to be about the same size, say, the size of a
dumpster.

First, is this true?

Second, is there any reason for this? In particular, I am surprised
there have not been more efforts to build very small probes.

Launch vehicles seem to scale badly at small scales (high surface
area, and I have a vague sense that building a small pump is hard), but
it seems much less obvious to me once the thing is in LEO. In
particular, it seems to me that solar thermal rockets could scale very
well.

The image I have in my head is a probe, mass on order of 100 grams
plus a few hundred grams liquid hydrogen fuel. (If the fuel tank is
small, perhaps it can hold high pressure gas instead of liquid?).
Communication probably done via laser, to avoid the need for a large
antenna.

Does anyone have an idea for how small the "basic necessities" can be
made - for example, some type of navigation system (star camera?), a
computing platform, and communication equipment?

I am even more unclear about what mission such a beast would be good
for; vague ideas that come to mind are investigating asteroids,
flythroughs of comet tails, and sample return of interplanetary media.
My hope would be that, since launch costs would be very low, many of
these things could be sent out - I would imagine there would even be a
"market" for lots and lots of medium quality photos of small moons.

As far as I know, every deep space probe we have ever launched has
been a one-off; these microprobes would have a significant advantage
economically, since they could be produced in larger runs. On the
other hand, ground support for 100 small probes might be much more
expensize than the equivalent for one large probe.

I have tried and so far failed to imagine how to get something this
size onto a planetary surface; it would seem to me to be very valuable
scientifically if we could scatter several hundred very small probes
across Mars, Europa, or other trendy locations.

Surely this idea has been had before.. but on the other hand, we are
better at making small things than ever before.

--Dave and Hank Patterson


SMART-1 exploited miniaturization to make a smaller probe.
http://sci.esa.int/science-e/www/are...cfm?fareaid=10
It is not close to 100 grams, though.

--
Hop David
http://clowder.net/hop/index.html

dave and hank patterson wrote:
From my rather small knowledge of deep space probes, it strikes me
that they all seem to be about the same size, say, the size of a
dumpster.

First, is this true?

No, e.g., for Mars probes compare Viking to say Mars Odyssey, or more
currently, compare Mars Odyssey to the Mars Reconnaissance Orbiter
launching in August. For recent probes in general, compare Cassini to
Lunar Prospector.

Second, is there any reason for this? In particular, I am surprised
there have not been more efforts to build very small probes.

Size depends on a number of factors -- science goals, instrument design
to meet the goals, budget, mission design (e.g., flyby vs. orbiter,
lander vs rover), technology (current technology allow for smaller
spacecraft to meet a given set of science goals vs technology from say
20 years ago).

There have been some small deep space probes, e.g., Deep Space 2 to put
2 coffee can sized probes on Mars. Deep Space 2 was a poor shadow of
the proposed MESUR program which would have put over a dozen landers
across Mars with 4 or 5 launches. Unfortunately, Deep Space 2 failed
which did not help proposals for additional very small Mars probes.


Launch vehicles seem to scale badly at small scales (high surface
area, and I have a vague sense that building a small pump is hard), but
it seems much less obvious to me once the thing is in LEO. In
particular, it seems to me that solar thermal rockets could scale very
well.

The image I have in my head is a probe, mass on order of 100 grams
plus a few hundred grams liquid hydrogen fuel. (If the fuel tank is
small, perhaps it can hold high pressure gas instead of liquid?).
Communication probably done via laser, to avoid the need for a large
antenna.

100 grams is really small. Even today, one science instrument masses
over 100 grams. With traditional design, spacecraft structure, fuel,
power, command/control, communications and data processing HW take up a
large part of the spacecraft mass.


Does anyone have an idea for how small the "basic necessities" can be
made - for example, some type of navigation system (star camera?), a
computing platform, and communication equipment?


Technology is allowing proposals for "sciencecraft" designs which
integrates the support HW into the science instruments to reduce mass.

I am even more unclear about what mission such a beast would be good
for; vague ideas that come to mind are investigating asteroids,
flythroughs of comet tails, and sample return of interplanetary media.
My hope would be that, since launch costs would be very low, many of
these things could be sent out - I would imagine there would even be a
"market" for lots and lots of medium quality photos of small moons.


A large number of small spacecraft (not quite 100 gram size) is useful
for coverage of wide areas or large numbers of bodies with different
characterisitcs. As for launch costs, it may be cheaper to launch a
larger number of probes on a single launcher provided the probes are
all going to same general vicinity.

As far as I know, every deep space probe we have ever launched has
been a one-off; these microprobes would have a significant advantage
economically, since they could be produced in larger runs. On the
other hand, ground support for 100 small probes might be much more
expensize than the equivalent for one large probe.


Ground support costs may or may not be much more expensive for one
large probe than for a lot of smaller ones. Operattions costs depend
on a lot of factors.

I have tried and so far failed to imagine how to get something this
size onto a planetary surface; it would seem to me to be very valuable
scientifically if we could scatter several hundred very small probes
across Mars, Europa, or other trendy locations.

Surely this idea has been had before.. but on the other hand, we are
better at making small things than ever before.

--Dave and Hank Patterson

A system for 1 pound spacecraft is being planned:
www.microlaunchers.com . A major set of flights will be for fly-by
photos of NEO's like 2004-MN4. The website is now a summary of a
presentation given last April at Space Access Society conference in
Phoenix. It's definitely feasible.

Another practical design constraint that sets the size of a spacecraft
is the fact that, in most cases, it has to fit within the launch
vehicle payload fairing. The spacecraft may have solar panels, booms,
or other appendages which are deployed after launch, but it all has to
fold up to fit within the payload shroud.

Martin