‘I think Franz and I would like to discuss it a bit first,’ von Braun ventured.
‘Of course!’ Heydrich waved his cigar jovially in the direction of his aide, who sprang to the table. ‘But I return to Prague tomorrow morning at seven. We do seem agreed on what needs to be done, so why not assume your decision will be favourable? Heh?’ He stood up, carelessly stubbing out his cigar on the tablecloth. ‘I am certain you will enjoy the advantages of working with the SD. Good night, gentlemen.’
‘Finding the moon will be relatively simple,’ von Braun went on. ‘The basic tools one uses are radio, radio direction finding, and the stars, which in effect become signposts that do not vary in the slightest – at least for our purposes. If one calculates the angular distance between the moon’s centre and a certain star before starting, it is possible to measure any deviation in the spacecraft’s flight path or orbit as one approaches one’s target simply by observing the angular distance.’
‘Orbit? I thought only planets travelled in orbits.’
Von Braun chuckled with an expert’s superiority. ‘They do, but any object travelling in space describes a curved trajectory. You see, the gravitational effect of the Earth, the moon, the sun, and even such major planets as Jupiter and Saturn, all affect the object, causing it to be pulled this way and that. If each of these gravitational tugs is balanced perfectly, the effect is really a curved line.’
‘I see.’ Heydrich nodded. ‘I assumed that once a craft reached airless space it merely coasted under the effect of the target planet’s gravity field.’
‘Basically it does, providing that such gravitational force is not overcome by one even stronger. Many people reading Professor Oberth’s book made that mistake.’
‘And how do you make certain that does not happen?’ There was a trace of annoyance in Heydrich’s voice. Clearly, Bethwig thought, he does not like being talked down to.
‘It is a matter of acceleration or speed,’ Bethwig broke in before Wernher could make matters worse. Heydrich had surprised him by showing genuine interest in the details of the project.
‘The correct speed must be selected to place the craft into the proper orbit. Too slow a speed will cause it to fall back to Earth. Too fast, and it will fall into the sun. Even faster, and it will escape the solar system altogether.’
‘Correct,’ von Braun broke in. ‘As the spacecraft approaches the moon, our observations become more accurate, allowing the speed to be adjusted. The occultation – disappearance of selected stars – behind the moon enables us to determine the exact course of the rocket as it approaches for a landing.’
In spite of the veiled threats of that evening three weeks before, Heydrich had since been polite and considerate, had even invited them to Hradcany Castle, his Prague headquarters, for a weekend. With brilliant autumn sunshine streaming across the pleasant garden beyond the french doors, Bethwig could feel tired muscles and tense nerves relaxing. That morning he and von Braun had strolled around Prague, and the mood of the city had certainly suggested that Heydrich was the model administrator he claimed to be. Bethwig recalled his comment about benevolence versus destructiveness. People seemed content, well fed and dressed, and there was none of the sullenness one encountered in Belgium, France, or even Denmark. The Czechs seemed to have adapted well enough to National Socialist rule – or Heydrich had adapted it to them.
Von Braun had begun to describe the rocket. ‘We have determined that a single-stage rocket, a vehicle designed to complete a mission as a single unit, is not practical. It would be far too large, given our present fuels, and cause insurmountable aerodynamic problems. So we have designed a three-stage vehicle, that is to say, three complete rocket vehicles stacked one atop the other. The first rocket, or stage, is the most powerful, as it must lift the combined weights of the others. Once its fuel is exhausted, it will be jettisoned, and the second stage will drive the rocket into space and temporary orbit around the Earth. Then, when it’s in the right position, the second stage will fire one last time, sending the third stage on its way to the moon. This final stage will coast along its assigned trajectory, firing its engines only to make course corrections and to brake itself to a landing on the moon. The rocket must then be refuelled from supplies brought up by drone rockets before it can return to Earth.’
Heydrich had leaned forward to listen. ‘You find it necessary to build three separate rockets? I thought the guiding principle in engineering was to make things as simple as possible. It would seem that the use of three rockets would increase the chance of failure thrice over.’
‘Actually, nine times, Herr Heydrich. But, as Franz said, we have not the fuels to build a rocket that can reach the moon in a single stage. In fact, even with three stages it will barely be sufficient. We must cut everything to the bone to save weight. Our navigational equipment, for instance, will be of the most primitive – a simple sextant. The smallest possible radio-direction-finding set will be used. And the pilot must be able to fix anything that goes wrong, as we cannot afford the mass to carry a spare set.’
‘Is it a matter of more money?’ Heydrich was smiling as he asked the question, but he was watching the young scientist closely.
‘No. Rather a matter of technology. Our fuel experts have been able to find only one or two fuel combinations that are more efficient than the alcohol and liquid oxygen mixture we now use, and they have drawbacks that negate their value.’
‘I am not certain I understand what you mean.’
‘For instance’ – Bethwig broke in – ‘the alcohol and liquid oxygen mixture we currently use approaches optimum in terms of energy obtainable from chemical fuels. The power, if you will, of a rocket fuel is measured in terms of specific thrust per second, which is simply the push per unit of fuel consumed. Liquid oxygen and alcohol provide a specific thrust of one hundred and eight kilograms per second. We could obtain a greater specific thrust with a combination of, say, liquid oxygen and hydrazine which provides one hundred and seventeen, or even liquid oxygen and liquid hydrogen which provides the greatest specific impulse of all chemical fuels, one hundred and fifty-two kilograms per second. But we do not have the facilities to manufacture or handle liquid hydrogen. Hydrazine would be ideal, but Germany does not produce it in sufficient quantities, and the resulting performance increase would not justify the added cost of developing a manufacturing capability. Above all, an engineer must be practical.’
Heydrich replied, with a trace of annoyance, ‘Yes, yes, I understand.’ He got up to pace the room as von Braun took up the briefing again, but it seemed to Bethwig that his patience was nearly exhausted. The more detailed the explanations became, the more restlessness the reichsprotektor displayed.
‘…will stand fifty-one point eight metres tall. At the base the first stage will measure nineteen point eight metres. The entire rocket will weigh 4,082,331 kilograms, nearly as much as a naval cruiser. We have designed a cluster of twenty-one rocket motors to provide a combined thrust of 3,401,942 kilograms. The motor will consume 3,985,230 kilograms of fuel in less than one hundred and twenty seconds. The second stage will have four motors providing a total thrust of 635,028 kilograms. The third stage will have a single motor providing 158,757 kilograms of thrust and will carry the crew and equipment. It will…’
‘Please, spare me a recital of further facts and figures.’ Heydrich heaved a sigh, then turned and smiled. ‘I really do believe you gentlemen know what you are doing.’