Bootstrapping is a very important aspect of getting the cost of starting
a tether down to an affordable prices.
The general idea of bootstrapping is to start by sending up a limited LEO tether
with an existing expensive rocket, and then use our reusable
rocket to grow the tether from there.
The initial tether will have limited solar power, limited thrusters,
and have a smaller payload weight limit. The limited solar power and
thrusters will mean it takes longer for the tether to replace
the energy used in picking up a payload. So we can not launch
payloads as often initially.
The SSTT rocket can be used even with this limited initial tether,
just not will full payloads. When a rocket flys with a smaller
payload, it can get to a higher velocity, so reducing somewhat
velocity/energy the tether needs to provide early on.
Since the SSTT rocket is reusable it will still be much
chaper to operate per pound even though it is only lightly
As we bring up more solar power and more thrusters we will be
able to launch more often. As we bring up a stronger tether
we can have higher tether tip speeds and lift larger payloads.
Starting out with a limited tether,
it only takes a few months to grow to a much larger
tether using the initial tether and the rocket designed
for the larger tether.
While bootstrapping, the orbit eccentricity, amount of ballast,
and tether strength determine the maximum load. The total
cargo per day is determined by the amount of solar power,
the thruster efficiency, and the delta-V being given to
The natural toss from the tether will have too much
energy to toss to itself, but it is possible to use
aerobreaking to reduce the payloads energy before
it is picked up by the ballast.
Current Costs vs Tether Lift Costs
Current cost is around $2,000/lb to get anything into orbit.
Our costs to lift something to orbit with a tether could be
very low, maybe $20/lb (though our price to others will be
higher). If we start with a very small tether and ballast
it will not initially be able to handle a full load from
our rocket. So initially the reusable rocket would fly only
partially loaded. If it was 10% full, our costs
could be on the order of $200/lb. This is still far cheaper
than existing ELVs. So we can save big if we can
start using our tether and SSTT right away.
As the ballast and tether get bigger, the rocket can lift
more on each flight.
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Copyright (c) 2002, 2003 by Vincent Cate. All rights reserved.