Re: Heavy Lift Design for Mining/Cargo Propulsion

Here is an interesting calculation...

185 kilonewtons of thrust (1/30th gee in previous example) from a
rocket engine with an exhaust speed of 20,000 km/sec uses propellant
at a rate of

F = dm/dt * V = 185,000 = dm/dt * 20,000,000 = 9.25 grams per
second

It will produce a power level of

P = 1/2 * dm/dt * V^2 = 0.5 * 0.00925 * (20,000,000)^2 = 1.85
terawatts.

About 10% of this energy will be in the form of UV radiation, which
will radiate in all directions behind the ship.

Eris is presently 96.7 AU from the Sun. So, the sun shines with a
brightness of 0.146 watts per square meter. About 1/10,000th as
bright as sunlight at Earth. The human eye can sense things
1/10,000,000th as bright as sunlight on Earth - so, we'll be able to
see things clearly - it will just be very dark by Earth standards.

Now, here are some interesting calculations...

The entire surface of Eris intercepts 0.22 terawatts, about 1/5th the
power output of the engine driving the ship even at 1/30th gee!!! The
light produced by the plasma will be generating half the energy of the
entire sun at Eris and it will be growing brighter as the ship
arrives!! When will the intercepted energy from the ship equal 0.146
watts per square meter?

Well, assuming the light is generally spread in a ball centered on the
ship, when the ship is 318 km from Eris, its exhaust will be brighter
than the sun at Eris - even at 1/30th gee. If the ship powers up to
1/10th gee - or more - to execute a landing on Eris - the light from
the plasma will increase - and the engine will be brighter than the
sun even if its 600 km or more from Eris. At two gees - the engine's
maximum output - the engine exhaust would be brighter than the sun
when the rocket is 2,500 km removed from Eris.

What would a 'sun' growing brighter and brighter for weeks at a time
occupying the same position in the sky do to Earth's environment?
Clearly, this will likely have noticeable effects on Eris as we
arrive.

It seems likely that Eris and other Kuiper belt objects, are likely
covered with solid methane, with solid water ice, and perhaps liquid
hydrogen and liquid helium oceans and clouds. Such low energy geology
and weather would likely be dramatically affected by an arriving
spacecraft like the one described - so care must be taken upon
arrival. Landing on these bodies with fusion rockets would be a
trick!

To put this in perspective, imagine creatures that had molten lava
flowing through their veins, made of tungsten and other refractory
materials breathing gaseous silica, flying a ship whose exhaust was so
bright, that when it got within 300 km of Earth the exhaust all by
itself was brighter than the sun and effected weather patterns over a
40,000 sq km area by evaporating all the water, and melting rocks down
to the mantle!

While taking 5 months to get there, and 5 months to get home might
make it unsatisfactory not to make a landing, it might be best to
orbit silently engines off - observing the system for a while before
attempting a 'planet' fall.


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Relevant Pages

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