1/ ANGARA module with RD191 engine ( one-quarter - RD171 engine). This modular system is suitable for LEO lifting capacity from 2 MT to 28 MT using 1-5 modules (for 28 MT with LOX/LH2 second stage). Angara system has been designed from the beginning as modular in above mentioned range and it would be difficult to increase further its capacity.

2/ ATLAS 5 module with RD180 engine ( one-half - RD171 engine). This modular system is suitable for LEO lifting capacity from 10 MT to more than 50 MT using 1-5 modules + LOX/LH2 second stage.

3/ ZENIT module with RD171 engine . Such modular system would be suitable for LEO lifting capacity from 20 MT to more than 100 MT using 1-5 modules + LOX/LH2 second stage.

4/ DELTA IV module with RS 68 engine. This modular system is suitable for LEO lifting capacity from 7 MT to 20 MT using 1-3 modules + LOX/LH2 second stage. I do not suppose further increasing of DELTA IV module number due to immense outer dimensions. It would be better to use either SRBs or LOX/Kerosen auxiliary boosters instead.

For medium and heavy lift capacity, the variant 2/ and 3/ seams to be the most suitable. It is necessary to design only tanks for second LOX/LH2 stages. For example Zenit module has trust 806.000 kgf and vacuum specific impulse Isp = 337 sec.

In comparison, F1 engine of Saturn 5 had trust 789.000 kgf and Isp 304 sec. A parallel cluster of five Zenit modules would have higher trust and much better fuel efficiency than first stage of Saturn 5. The length of the first stage would be 33m in comparison with 43 m of Saturn 5 first stage.

Second LOX/LH2 stage could be equipped with modern RS68 or RD 0120 engines and the result will be a more powerful booster than the Saturn 5. Such booster would allow the return on the Moon in one launch mode, similar to the Apollo project.

There is another outstanding feature of Zenit module - its fully automation of pre-start operations, including loading of relatively low-maintenance fuel. It enables to shorten necessary preparatory time to a fraction of that of any present rocket.

Serial production of such modules for Russia, ESA, ILS and SL would substantially reduce production cost. All these gains will reduce the overall cost of launch operations, making space flights more routine and cheaper.

Also five module version of Atlas 5 would be sufficiently powerful for operations for the return on the Moon in two starts launch mode. In such plan in first start, LSAM (Lunar Surface and Ascent Modul) + EDS (Earth Departure Stage) is launched to LEO and further to LLO (Low Lunar Orbit).

In second start, EDS + CEV with a propulsive capability for Trans Earth injection is also launched to LLO. On LLO, the CEV performs randezvous with LSAM, after which the crew transfers to the LSAM. Further operations are similar to the Apollo project. It would be also possible to perform first randezvous on LEO between powerful EDS delivered in the first launch and combined LSAM+CEV delivered in the second launch with further operations similar to the Apollo.

In US, to have powerful expandable booster to return on the Moon in one launch mode, it would be also possible to modify STS by placing SSME or RS68 engines under ET. In this case, it is necessary to realize that STS is 1.5 stage system only and the empty mass of ET + engines is app. 35.000 kg. This dead mass must be accelerated almost to the LEO velocity and the ratio between payload and dead mass is relatively poor.

Such ratio is justifiable for system where some expensive parts of dead mass are reusable (for example SSME). For expandable systems, the classic 2-stage configuration to LEO has the ratio much better.

Both Modular Launch Vehicles based on Atlas 5 or Zenit modules allow to create new powerful boosters for man space exploration with decades long operational life. Such modular conception would save billions of US$ and years of development.

Josef Pinkas, can be contacted via pinkasj at tiscali.cz

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