(1/2) Soviet manned Mars mission using nuclear/ion propulsion (long)
mlin...@aton.abo.fi
I have finally found some detailed information on Soviet plans
for manned Mars exploration. "Power-Propulsion Systems for
Orbital Nuclear Transfer" by Koroteyev et al. (ACTA
ASTRONAUTICA Vol.24 pp.181,1991). The authors compare the merits
of NERVA type nuclear thermal engines, a hybrid chemical/ion
propulsion system before finally settling for pure nuclear
electric (ion) propulsion. The Russians appear to have
consistently favored this low thrust, high Isp option since the
early 1970s; this in stark contrast to NASA's plans which have
mostly been based on high-thrust chemical or nuclear thermal
propulsion. The Soviet approach to manned Mars exploration is
both interesting and strikingly different. I will first
describe the mission and then discuss the merits and drawbacks
compared with American plans such as Mars Direct.
1.NUCLEAR POWER PROPULSION OPTIONS
----------------------------------
The Soviet option used a huge nuclear reactor generating up to
50,000kW -- 450 times more power than the International
Space Station's solar panels! In addition to producing
electrical power, the reactor's thermal output can be used to
heat liquid hydrogen propellant to 2800K if the nuclear-thermal
rocket (=NERVA) option is used. A 460-day two-way mission to
Mars orbit would have to start from a high 800km Earth parking
orbit due to the radiation hazard. The total mass would be 800
metric tons, including 495t of LH2 fuel, a 150t payload, a
70t reactor/propulsion module (200kW,200kN thrust,917s Isp).
The remainder is presumably LH2 tankage.
---
Option#2 would feature a chemical liquid oxygen/hydrogen
rocket (1.1mN thrust,480s Isp) for quick acceleration through
the Earth's radiation belts. A 260N nuclear-ion engine would
then provide the thrust for the remainder of the journey. Total
spacecraft mass would decrease to 700t (including 310t of
LOX/LH2 propellant plus 147t of lithium fuel for the ion drive)
but the total mission duration would increase to 615 days. The
required delta-Vs from an 800km parking orbit are 3.1km/s for
the chemical rocket plus 25km/s for the low-thrust transfer to
Mars orbit & return to Earth. Both missions (option#1 & 2)
would have taken place in 2018 and permitted a 30 day stay on
Mars.
2.NUCLEAR-ELECTRIC MARS SPACECRAFT
----------------------------------
The option finally chosen was a pure nuclear-electric system
using closed Brayton-cycle gas turbines working at 1800K
temperature for heat-to-electricity conversion.
The total travel time would be reduced to 320 days. In
addition, the spacecraft would weigh less (550 metric tons,
including 300 tonnes of xenon fuel). The delta-V would increase
to 47km/s, however.
---
An ASCII diagram of the spacecraft is shown below.
Mars
landing
vehicle
Radiators __
|_| | |
|_| | |
|_| | |
|> |_| _____ _ _____ |__|
=/|____________||_______________________________|_|/ \/ \/ \\__/
||/_\/_\/_\ooo||oooooooo\/\/\/\/\/\/\/\/\/\/\/\|_| || || ||__|
=\| ||-------------------------------|_|\_____/\_/\_____/ ||
|> |_| ||
|_| /\
|_| ==
|_| Mars
Reactor Ion thrusters Orbital
("o"=propellant tanks) Vehicle
habitation Earth
modules return
capsule
+airlock
--------------------------------------------
WEIGHT BREAKDOWN
--------------------------------------------
2 x 25mW reactors+radiation shield.......14t
2 x turbogenerators......................15t
2 x heat exchangers .....................18t
Radiators................................22t
Control system............................1t
Ion engines .............................10t
Boom (60kg/meter).........................6t
Fuel tanks................................7t
Refrigerator+misc. .......................7t
Xenon fuel..............................300t
Mars Orbital Vehicle (MOV)...............80t
Mars Landing Vehicle (MLV)...............60t
Earth Return Capsule.(ERV)...............10t
--------------------------------------------
550t
An interesting feature of the propulsion system is that the
thrust can be increased (at the expense of a decreased Isp /
higher propellant consumption) for major maneuvers that have
to be carried out quickly. Most important among these is the
initial departure from parking orbit;the spacecraft "spirals
outwards" throught the van Allen belts to an ~185,000km
circular orbit in just 7.5 days. From there on, the engines
operate in a more economical high-Isp / low-thrust mode.
(Ion thrusters are very efficient because their
exhaust velocity is high, so less fuel will have to be carried
on board. The main drawback is the low thrust which means the
engines will have to be fired continuously for days or months.)
---
This "all-up" mission would begin in May 2018 and could
deliver a 4-crew to Mars orbit, where two cosmonauts would
descend to the martian surface in the MLV for 2-3 weeks of
exploration. However, it would be more economical to launch
an UNMANNED CARGO SPACECRAFT on a one-way mission in 2016,
carrying the MLV plus a "temporal research [orbital space-]
station". Payload mass in Mars orbit would be 150t, but the
total mass in LEO would decrease to 280t. This is because
the cargo spacecraft would not have to carry fuel for the
return trip and because a slower, more economical 320-day
trajectory could be used. Only one 25mW reactor would be
required so the mass of the propulsion system is reduced by
almost 50%.
The MANNED SPACECRAFT (sans MLV and carrying 53t less propellant)
would depart from Earth in May 2018. Below is a timetable for
that mission:
Thrust Exhaust Duration Propellant
velocity consumed dV Remarks
(=Isp/0.0098)
-------------------------------------------------------------
3500N 20km/s 7.5d 113.5t 6.0km/s 800km->185,000km
Earth orbit
1000N 90km/s 17.5d 16.5t 4.7km/s ->1.25AU from Sun
(60 day interplanetary coast period;)
1000N 90km/s 30.0d 29.0t 8.9km/s 1.38 to 1.39AU distance
1500N 50km/s 5.0d 13.0t 2.4km/s Mars orbit insertion
(21 days of Mars exploration in October 2018)
1500N 50km/s 5.0d 13.0t 2.4km/s Departure from Mars
3500N 90km/s 50.0d 48.0t 19.0km/s Transfer from 1.38
to 0.78AU
(100 day coast at 0.72 to 0.78AU distance)
1000N 90km/s 12.0d 11.5t 5.2km/s* Earth arrival,March 2019
-------------------------------------------------------------
~320 days 244 tonnes 45km/s total delta-V
3.COMMENTS / POSTSCRIPT
-----------------------
Nuclear-electric propulsion appears to reduce the mass that
has to be launched into low Earth orbit by a factor of 1.5-2
vs. chemical rockets for unmanned cargo missions. This does
not necessarily translate into reduced costs, however -- the
reactor+ion thrusters appear to push the state-of-the-art in
many ways (e.g. power-to-mass ratio) and xenon is both rare
and expensive.
---
The manned example would not be practical using chemical propulsion;
NASA's 15-month "Sprint" proposal from 1986 would have provided
a similar 3-week Mars exploration opportunity but the required
delta-V (7km/s+ to Mars, 4km/s to Earth) was much too high for
a single spacecraft. Like the Soviets, NASA would have launched
part of the unmanned payload in advance, on a more economical
trajectory.
---
In the wake of the Chernobyl disaster, the Soviets wisely
rejected the huge space reactor concept on grounds of political
risk. Consequently it was decided to investigate if large
solar-dynamic & photovoltaic systems could power the ion
thrusters instead. The favored option (described by David
Portree [ http://members.aol.com/dsfportree/explore9.htm ])
featured two giant 40,000 square meter solar panels and
the required technology could have some interesting applications
for solar power satellites. I will discuss this in Part 2
of this article.
MARCU$
-----== Posted via Deja News, The Leader in Internet Discussion ==-----
http://www.dejanews.com/ Now offering spam-free web-based newsreading
Allen Thomson
In article <6je8ro$805$1...@nnrp1.dejanews.com> mlin...@aton.abo.fi writes:
>I have finally found some detailed information on Soviet plans
>for manned Mars exploration. "Power-Propulsion Systems for
>Orbital Nuclear Transfer" by Koroteyev et al. (ACTA
>ASTRONAUTICA Vol.24 pp.181,1991).
[snip]
Thanks for posting that -- Koroteyev of NIITP and the
more senior V.M. Iyevlev were prominent in the fairly extensive
and little appreciated Soviet program(s) to develop nuclear power
for use in space. At one time, they were working fairly seriously
on a gas-core rocket with hydrodynamic/magnetic fuel containment
that would have given both high thrust levels and high-ish Isp
(in the several tens of km/sec range -- several thousand seconds for
English speakers).