Re: antimatter rockets

On Jan 3, 6:58 pm, Sylvia Else <syl...@xxxxxxxxxxxxxxxxxxx> wrote:
Willie.Moo...@xxxxxxxxx wrote:
www.engr.psu.edu/antimatter/Papers/NASA_anti.pdf

Doesn't paint an attractive picture for pure matter-antimatter rocket.

The possibility of anti-matter catalysed fusion rockets seems less of a
dream.

Sylvia.

They're all dreams sweetie when it comes to anti-matter - as opposed
to the other stuff I've written elsewhere.

A shaped block of tungsten illuminated with an anti-matter beam would
form a dandy solid core rocket - very similar to NERVA with no nuclear
materials.

The melting point of tungsten is 3,695K
The boiling point of tungsten is 5,828K

Multiplying 3,500K by 14.3 kJ/kg-K obtains 50.5 MJ per kg of gas.
Solving for gas velocity obtains 10,005 m/sec which resolves to 1,019
sec Isp.

This appears to be the limit for a solid core rocket heating hydrogen.

1,019 sec Isp, requires 10 kg/sec to obtain 100 metric tons thrust.
This also requires 500 MW heat source which is provided by 2.8 ug per
second of antimatter.

With a 50:1 thrust to weight, this rocket masses 2 metric tons. With
a lift-off gee force of 1.35 gees vehicle mass is 74 metric tons.
With an ideal velocity of 9 km/sec and an exhaust speed of 10 km/sec
propellant fraction is 59.34% - this translates to 43.9 tonnes. With
6% tank weight, that's 2.7 tonnes for tankage and plumbing. Total
structure faction is 15% - or 11.1 tonnes

GLOW 74.0 tonnes
LH2 49.9 tonnes
Struct 11.1 tonnes
2.0 tonnes - engine
2.7 tonnes - tank
Payload 13.0 tonnes

A 5 engine system - configured like the Saturn V moonrocket - though
these are far smaller (1/15th) than the F1 - could loft 65 metric tons
into LEO.

That payload could of course be... the single stage rocket described
here... slightly less than LEO,

The second stage which would impart an additional 9 km/sec to the 13
tonne payload.

Which could take it to the moon, land it, and return it to Earth -
with recovery of all components.

Ditto for Mars.. with aerobraking at Mars.

13 metric tons is nearly the fullup weight of the Apollo LEM
or the size of the Manned Orbiting Laboratory (MOL)

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19650076610_1965076610.pdf

Sufficient payload to carry up to 7 passengers/crew on trips to the
Moon and Mars.

Higher exhaust speeds require higher temps. This requires gas and
plasma reactors.

Rather than worry about steady state gas and plasma masses we could
steal a trick from the nuclear pulse people, where anti-protons are
injected into a containment which then leaks them out into a small
tungsten block which is vaporized. The plasma/gamma pulse is
reflected off ablative walls - which propel the vehicle - pulse
fashion. The tungsten and ablative material is consumed as part of
the propellant mass. Up to 40 km/sec may be produced in this way..
thrust to weight suffers - dropping to 10:1 - but propellant mass
improves.

A 100 metric ton thrust engine masses 10 metric tons, and has an
exhaust speed of 40 km/sec. To achieve 9 km/sec ideal velocity
requires 20.15% propellant fraction. The same 1.35 gee lift off
thrust means again a 74 metric ton vehicle. 14.9 metric tons of
propellant. Another 8.1 tons of structure - gives us 41 metric tons
of payload.

Alternatively, taking the difference between 13 tonnes and 41 tonnes -
as propellant - adds 28 tonnes to the propellant mass. This increases
propellant fraction from 20.15% to 57.98% which increases ideal
velocity from 9 km/sec to 34.67 km/sec - which gives a single stage
vehicle Omni-planetary capability. That is, a single stage could take
off from Earth and fly to Mars, or the Moon, land and return to Earth.

.

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