A spot of light launch

I went to an interesting talk a few weeks ago by Jordin Kare
(part of the Space Access conference).

He talked about a laser launch system that was based on
shining lasers at a hydrogen powered rocket vehicle that
has a heat exchanger on it that reaches 1000C. The hot
hydrogen squirts out the back through a conventional
nozzle. No oxidiser or turbopumps are required. The
estimated ISP is about 600 seconds (this is 1/3 more
than the Shuttle manages).

People like Leik Myrabo planned to use big pulsed lasers
for this, but Jordin suggests that semiconductor lasers
are much cheaper- they're currently running at about
$1.5/watt and dropping at about 30% per year(!); and they're
not pulsed, but then a heat exchanger doesn't need or
want pulsed lasers. You'd need a fairly big farm of
telescopes each with aiming hardware all pointing
at the launch vehicle; but that's thought quite
doable; and not outrageously expensive.

Each kg of payload needs about 1MW to reach orbit.

He was proposing a vehicle with a payload of about
140kg; so that's about 300 million in lasers or so;
which is a fixed one-time cost, so would be amortised
over each launch; and it can launch a LOT.

The system can fire every 15 minutes, and can launch
30,000+ times per year at an estimated cost of about
$100/kg. That's 3000 tonnes per annum.

There are some minor issues with aiming, but they're not
thought serious. The launch trajectory is a bit interesting
too- if you used a normal trajectory you'd be over the
horizon before reaching orbit. Instead, there's a special
one that goes unusually high.

Another issue is that hydrogen engines are very efficient
(high ISP), but don't give particularly good thrust; Jordin
is proposing use water injection at low altitude to
increase the thrust.

He thought the system would cost maybe $1-2 billion including
development costs.

My take on it is that he needs to scale his ideas up some-
300kg is about enough for a person in a space suit to make
orbit and return safely. But you can't really complain
about the price. If my estimates are right, this would
cost about $100,000 per person to orbit and back again.

The system could be built within 5 years including R&D.

Personally, this looks like the most promising system I have
seen. The point about semiconductor lasers now becoming
cheap cannot be overestimated. The increase
in performance of laser assisted hydrogen engines is
crucial- at an ISP of 600 seconds SSTO becomes much closer
to reality, and many system cost savings are realised.

If enough cost savings are found then we get to go to
space... this looks like it might be the way.

--
- Ian Woollard (ian.woollard@...)

"Is a planetary surface the right place for an expanding
technological civilization?"
- Gerard O'Neill