[ExI] Space Project (power satellites)

Keith Henson hkeithhenson at gmail.com
Fri Aug 7 22:35:33 UTC 2020

Stuart LaForge <avant at sollegro.com> wrote:

> Have you run the numbers for constructing power satellites at
earth-moon L1, and then moving them into place?

For parts from earth, flying them to L1 and back to GEO would cost far
too much delta V.

> That would be above
the Van Allen radiation belt. Another possibility might be to
construct them in polar orbit. Then the astronauts would only be in
the belt 1/3 of the time.

The radiation is still way too high.  Plus it is much more expensive
to launch to polar orbit since you can't take advantage of earth's
rotation.  Plus the amount of delta-V it would take to plane change
from a polar orbit to GEO is excessive.

> Since they would know when they would be
entering the belt, they would be able to seek shelter inside small
shielded compartments or something. I haven't done any calculations on
these ideas, so I am just throwing them out there as suggestions.

Makes me realize how much unstated background in involved with this topic.

Adrian Tymes <atymes at gmail.com> wrote:

> Data source, please?

Table in Wikipedia, simple spreadsheet.  This problem has been
recognized since the late 78s.

> That a single satellite going LEO->GEO will on
average be hit 40 times seems way higher than is supported by the data I am
aware of - which is that most satellites going from LEO to GEO get hit zero

Comm satellites have dimensions of meters and an area of tens of
square meters.  They also go up fast, a few hours.  Power satellites
have dimensions in the 10 km range, areas in the tens of square km,
and (if self powered) take weeks to months to go from LEO to GEO.


> What are you thinking they are built of,

Invar perhaps.

> and how do those components get
there in ways that fully constructed satellites wouldn't?

> For that matter, how are you thinking the components get to LEO, in ways
that are collectively cheaper than ground assembly then launching the whole
thing to LEO?

Ah . . . A power satellite has km scale dimensions, a mass of around
30,000 tons and is flimsy.  I don't think a multi km faring or a
rocket big enough to put 30,000 tons in LEO is in the cards.

> The current baseline logistics is to collect parts in a 300 km orbit,
> then use a recycling tug with chemical fuel to get them out to the
> construction site at 2000 km (densely packed so they present a small
> target to getting hit).  It takes (IIRC) 827 m/s for a Hohmann
> transfer from 300 km out to 2000.  The fuel burned increases the cost
> of parts (and reaction mass) at the construction orbit by about 20%
> over the cost at 300 km.

Have you looked into ion engines for the tug instead of chemical engines?

Ion engines are of such low thrust it would spend years going up.
Arejets seem to be better suited to the task.

Adrian Tymes <atymes at gmail.com> wrote

> I wonder if there's enough data to estimate the cost of setting up a lunar
construction facility, building the satellites there, then launching (fully
assembled) from the Moon to GEO.

I would say this is way beyond what can be done with existing engineering.

 Dan TheBookMan <danust2012 at gmail.com> wrote:

> Bigger target though. SSPSs are really big compared to even the biggest satellites, no?

Close to a million times larger.

Adrian Tymes <atymes at gmail.com> wrote:

> Not nearly big enough to get hit an average of even once per trip, let
alone 40, if Keith means the designs I think he means.

You also need to factor in that they take weeks rather than an hour to
go through the junk.

> Especially if the trips are plotted to avoid tracked debris; I was
literally just yesterday looking at the US government's latest service to
check such trajectories and confirm they'll be free of known debris, and
they have access to good enough radar to track almost anything large enough
to matter.  (Acknowledging that "large enough" is very small, given orbital
velocities.  They still track it.)

It will not be hard to keep from hitting the big stuff.  But there is
just too much small stuff to avoid it.


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