|Class: Manned. Type: Mars Expedition.
Mars. Nation: USA. Manufacturer: Von Braun.
Wernher von Braun made the first engineering analysis of a manned mission to Mars in 1948. He published his calculations in 1952, and they subsequently reached a wide audience in Collier's magazine, a series of books, and the Walt Disney television program. What is astonishing is that Von Braun's scenario is still valid today.
In 1948, with the US Army's V-2 test project winding down, Wernher Von Braun was ensconced in isolated Fort Bliss. He had, unusually, some time on his hands. He occupied himself by writing a novel concerning an expedition to Mars, grounded on accurate engineering estimates. As an appendix to the novel he documented his calculations. The novel was reportedly awful and has never surfaced. But Von Braun used the calculations as the basis for a lecture at the First Symposium on Spaceflight held at the Hayden Planetarium in New York on Columbus Day, 1951. Von Braun's concepts, illustrated by magnificent Chesley Bonestell paintings, were made available to a large public with the publication of a series of articles in Collier's magazine beginning in February 1952. This was subsequently released as a book, 'Across the Space Frontier', in 1953. The technical appendix was published in German as Das Marsprojekt in 1953 and in English in America in 1962 as The Mars Project. Refined designs were presented in 1956 in 'The Exploration of Mars' and reached an audience of 42 million Americans in a series of programmes televised on the Walt Disney show. Von Braun's concepts were known to a wider audience than any other of the period. No other series of articles, books, and programmes did more to popularise the idea of manned space travel before Sputnik.
Das Marsprojekt was the first technically comprehensive design for a manned expedition to Mars. Von Braun envisioned not a simple preliminary voyage to Mars, but an enormous scientific expedition modelled on the Antarctic model. His Mars expedition was to consist of 70 crew members aboard ten spacecraft - each spacecraft with a mass of 3720 tonnes! To assemble this armada in earth orbit, Von Braun proposed a fully recoverable, reusable three-stage launch vehicle, which was designed to deliver 25 tonnes of cargo plus 14.5 tonnes of 'excess propellant' for the Mars fleet with each launch. Assembly of the expedition would take 950 launches of 46 these reusable space shuttles over eight months from a very busy base at Johnston Island in the Pacific Ocean. The first and second stages would splash down under parachutes 304 and 1459 km downrange, then be towed back to the launch site by a tug. The winged third stage, after dumping its cargo at the assembly point and pumping its excess propellants to the Mars ships, would glide to a landing on Johnston Island. All three stages would be refurbished at the island, stacked, and reused.
The expedition would use minimum-energy Hohmann trajectories to Mars and return, requiring a long stay at Mars, which was certainly appropriate for an expedition of this scale. The expedition fleet would consist of seven passenger ships and three cargo ships, all of the same starting mass. The passenger ships were equipped with 20-m-diameter habitation spheres for ten men per ship, and an extra 356.5 tonnes of propellant for the return trip home. The three unmanned cargo ships would each carry a 200-tonne winged lander and 195-tonnes of reserve supplies to Mars orbit, and then be left there. There was no thought of automated precursor missions in the days before solid-state electronics. The mission profile was as follows:
For both the launch vehicle and the Mars ships, Von Braun selected nitric acid/hydrazine propellants. These were corrosive and toxic but had the advantage of being storable without refrigeration -- an absolute requirement for the Mars craft, which would spend up to two years in earth orbit during assembly, followed by the three-year trip to Mars and back. Common engines were used in the upper stage of the launch vehicle and the Mars craft. These very conservatively used a combustion chamber pressure of 15 atmospheres (as in the V-2 engine).
Ideal engine performance was based on combustion chemistry and gas dynamics calculations. 'Based on experience', Von Braun expected efficiency losses of 10% for the high-expansion ratio engines. Specific impulse and thrust for the engines was not expressed in common modern terms, which causes some confusion in the literature. The figures given are the specific impulse at the condition of the ambient atmospheric pressure equalling the nozzle exit pressure. The figures adjusted to vacuum specific impulse terms indicate the Mars expedition engines would have a specific impulse of 297 seconds, a very respectable value not achieved in flight for a storable propellant engine until 1962. Von Braun used a constant thrust/weight value of 69:1 in calculating the engine mass for all stages. This again was conservative and in fact would be nearly met on the next US large engine design after the V-2, the Redstone. Von Braun's engine used a separate propellant (hydrogen peroxide) to drive the engine pumps.
Von Braun minimised the scope of the effort, noting that the 5,320,000 tonnes of rocket propellant required for the entire enterprise was only 10% of the amount delivered in the Berlin Airlift and would cost only 4 million dollars. On the other hand, he also noted the many unknowns at the time he was writing. The flux of cosmic rays and meteoroids beyond the earth's surface was completely unknown in 1948. Von Braun recognised the threat of cosmic radiation. But the greater danger of solar radiation was not known. The Van Allen radiation belts, created by the earth's magnetic field which shielded the earth from high energy solar radiation, were not discovered until 1958. So the positioning of the spacecraft assembly at a 1730 km altitude earth orbit, deep in the lower Van Allen belt, would not have been possible. Furthermore, more radiation protection would have to be provided the crew on the journey to Mars and on the Martian surface than Von Braun recognised.
Von Braun did realise that there might be danger of long exposure of humans to zero-G. He suggested that if this was found to be the case, he suggested tethering the passenger ships together, and spinning them with tethers to produce artificial gravity during the coast to Mars and period in Mars orbit. Alternatively, he proposed 'gravity cells', separate dumbbell-shaped spacecraft deployed during the cruise, in which the crew would spend several hours a day under gravity to ensure fitness. It was clear as he thought of his convoy as a community in space, with lots of daily traffic between the spacecraft.
At the time there was no clear technical solution to the problem of interplanetary navigation. Von Braun presumed the crew would take star and planetary sightings during the voyage, calculate their deviation from the planned course, and make appropriate manoeuvres. For this purpose a relatively enormous - 10% - propellant reserve was included. This would cover any contingencies, as well as the necessary orbital plane change manoeuvre required en route and not separately identified by Von Braun.
As contingency against all the unknowns, Von Braun equipped his cargo ships with a 195 tonne reserve for additional equipment, supplies, and surface probes. This was a huge amount, and certainly enough to build the radiation shelters, gravity cells, and other known dangers.
And finally, like all space visionaries before Mariner
4 in 1965, Von Braun did not know that the Martian atmosphere was only
one tenth the density estimated, and that there was not multi-cellular
life on the surface, as astronomers were sure they had observed from earth.
His graceful long-winged landing boats could not have made a horizontal
landing on the surface. But even this was not insurmountable. Von Braun's
glider would have had been subsonic at the 47 km altitude of his assumed
atmosphere, corresponding to the actual surface pressure of Mars. An alternate
landing scenario could have been to jettison the wings just over the surface,
deploy a drag chute, and bring the fuselage/ascent stage down to a vertical
rocket-powered landing on the surface. Von Braun's design had the margins
and flexibility to handle even this worse-case contingency.
Von Braun Mars Expedition - 1952 Mission Summary:
The first design for a manned Mars orbiter based on engineering analysis. 10 passengers would be housed in a 20-m-diameter sphere during the 963 day mission to Mars, in Mars orbit, and back to earth. The Passenger Vessel would perform four major maneuvers: Trans-Mars Injection (3860 m/s), Mars Orbit Insertion (2200 m/s), Trans-Earth Injection (2200 m/s), and Earth Orbit Insertion (3600 m/s).
Each crew member was allowed 120 kg of personal baggage. Consumable supplies totaled 12 tonnes of oxygen, 8 tonnes of food, 2.5 tonnes of food containers, 13 tonnes of potable water, 2 tonnes of utility water. Additional utility water would be extracted from the cabin atmosphere during the mission, sterilised, and re-used. Final empty weight of the passenger vessel in earth orbit at the end of the mission would be only 50.5 tonnes, only 1.4% of the 3720 tonne departure mass.
Crew Size: 10. Design Life: 1000. Length: 41.00 m (134.00 ft). Basic Diameter: 20.00 m (65.00 ft). Mass: 3,720,000 kg (8,200,000 lb). Structure Mass: 11,800 kg (26,000 lb). Reaction Control System: 1,000 kg (2,200 lb). Navigation Equipment: 3,000 kg (6,600 lb). Electrical Equipment: 2,000 kg (4,400 lb). Communications Systems: 1,000 kg (2,200 lb). Crew Seats and Provisions: 5,500 kg (12,100 lb). Crew mass: 800 kg (1,760 lb). Miscellaneous Contingency: 3,700 kg (8,100 lb). Environmental Control System: 20,000 kg (44,000 lb). RCS Fine No x Thrust: Flywheels. Main Engine: 8,700 kg (19,100 lb). Main Engine Thrust: 1,960.000 kN (440,620 lbf). Main Engine Propellants: nitric acid/hydrazine. Main Engine Propellants: 3,662,500 kg (8,074,400 lb). Main Engine Isp: 297 sec. Spacecraft delta v: 12,000 m/s (39,000 ft/sec).
Using the same basic systems as the Passenger Ship, the Cargo Ships would substitute a 200 tonne Landing Boat for the surface expedition and 195 tonnes of other supplies (consumables, spares, atmospheric and surface probes. The Cargo Ships would be left behind in Mars orbit and perform just two major maneuvers: Trans-Mars Injection (3860 m/s) and Mars Orbit Insertion (2200 m/s).
Design Life: 1000. Length: 64.00 m (209.00 ft). Basic Diameter: 20.00 m (65.00 ft). Mass: 3,720,000 kg (8,200,000 lb). Structure Mass: 6,300 kg (13,800 lb). Reaction Control System: 1,000 kg (2,200 lb). Navigation Equipment: 1,500 kg (3,300 lb). Electrical Equipment: 1,000 kg (2,200 lb). Communications Systems: 500 kg (1,100 lb). Payload: 395,000 kg (870,000 lb). RCS Fine No x Thrust: Flywheels. Main Engine: 8,700 kg (19,100 lb). Main Engine Thrust: 1,960.000 kN (440,620 lbf). Main Engine Propellants: nitric acid/hydrazine. Main Engine Propellants: 3,306,000 kg (7,288,000 lb). Main Engine Isp: 297 sec. Spacecraft delta v: 6,200 m/s (20,300 ft/sec).
The first design for a manned Mars lander based on engineering analysis. The enormous glider would have a wingspan of 153 m, and land on Mars horizontally either on skis, skids, or wheels on a prepared runway. The fuselage, which formed the ascent stage, would then be winched vertically for the return to the fleet of mother ships in Mars orbit after 400 days on the surface.
There were two kinds of landing boats. The first sent to the surface from Mars orbit would separate from the Cargo Ship in a 1000 km altitude circular equatorial orbit. The 200 tonne thrust engine would fire for 17.2 seconds in a 173 m/s deorbit burn, setting the perigee of the descent ellipse at 155 km. The re-entry calculations were based on the Martian atmosphere having a surface pressure 0.084 bar (ten times more than the actual figure that would only become known in 1965).
The long gliding re-entry, on immense wings of 2810 sq m area, would last for 86 minutes and extend over 12,655 km, over half way around the planet. The glider had the cross range to reach any point on the Martian surface, from the equator to the polar ice caps. Peak heating during re-entry would be 649 Kelvin, and maximum g-forces would be only 0.12. The glider would become subsonic at 39 km altitude, giving it plenty of time to select a suitable landing spot. It would make a horizontal landing on skis on one of the polar ice caps. This was a one-way trip -- the crew of the first landing boat had no means of return to Mars orbit. Instead of an ascent stage, the glider's payload was 125 tonnes of pressurised habitat/crawlers. The crew of the glider would travel 6500 km in 80 days in their Mars crawlers to the Martian equator, where a base and landing strip are set up. Presumably this was a worst-case scenario - if a suitable landing site nearer the planned base could be found, the first landing boat would be targeted there rather than the ice caps.
The two remaining landing boats would touch down on wheeled landing gear at the prepared strip. The fuselages of these gliders acted as ascent stages that provided the means for return to the expedition's spacecraft in Mars orbit. After the landing, the fuselages would be pivoted upwards, ready to lift-off in case an emergency departure is required. The equatorial orbit of the expedition fleet meant that launch opportunities were available every 2 hours and 26 minutes. 50 of the expedition's 70 crew would be sent to the surface on the three landing boats. They would spend 400 days exploring the surface of Mars, living in inflatable quarters, and making long surveys of the surface away from the base in the crawlers.
At the appropriate time, the crew would lift-off in the two ascent vehicles and rendezvous with the seven passenger ships in orbit. The ascent stages would have a launch mass of 138 tonnes. The burn into an elliptical transfer orbit would require a delta-V of 3700 m/s and 118 tonnes of propellant. The burn would take 147 seconds, placing the stage in a 125 km x 1000 km equatorial transfer orbit. The circularisation burn near the fleet of passenger ships would be 180 m/s and require 1.8 tonnes of propellant. Transfer of the 50 astronauts and the 5 tonnes of material each ship would have returned from the surface would be done between the ascent vehicles and the passenger ships using the fleet's 3.5 tonne space boats. The ascent stage, abandoned in Mars orbit, would have an empty mass of 19 tonnes.
Crew Size: 17. Design Life: 750. Length: 22.00 m (72.00 ft). Basic Diameter: 4.70 m (15.40 ft). Span: 153.00 m (501.00 ft). Mass: 200,000 kg (440,000 lb). Payload: 12,000 kg (26,000 lb). Main Engine: 8,700 kg (19,100 lb). Main Engine Thrust: 1,960.000 kN (440,620 lbf). Main Engine Propellants: nitric acid/hydrazine. Main Engine Propellants: 125,000 kg (275,000 lb). Main Engine Isp: 297 sec. Spacecraft delta v: 4,100 m/s (13,400 ft/sec).
Bibliography and Further Reading