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The GIANT mistake of the Orion's SM
While waiting for a "Stumpy" or "Direct" version of this article... I wish to explain here my opinion about the Orion's Service Module design that (I think) has a GIANT MISTAKE built-in, from scratch!!!
But (first) I must start from the Apollo's vehicles (left) their specs and the way they have accomplished the moon missions.
As you can see from the image, the Apollo's Service Module lenght was TWICE the capsule (three times from the engine) with a weight of 24.5 mT and over 18.4 mT of it was the propellants' weight (the total Apollo CSM weight was 30.3 mT) while the Lunar Module's total weight was only 14.7 mT with 10.5 mT of propellants' weight (exactly, 10.15 mT the Descent Stage's total weight, 8.1 mT of it for propellants, and 4.55 mT the Ascent Stage, 2.3 mT of it for propellant).
The Apollo CSM (and propellants) weight was TWICE the weight of the Lunar Module (and propellants) since the CSM was designed to perform (both) the Lunar Orbit Insertion (to brake the full CSM/LM and enter the lunar orbit) and the Trans Earth Injection (to bring back to Earth the Apollo CSM) while the LM's propellants was sufficient only for its lunar landing and departure.
In the ESAS plan, the vehicles' design has changed very much in favour of a smaller Service Module (able to perform ONLY the TEI) and a bigger LSAM (with bigger and heavy tanks) that will have sufficient propellants for the Orion/SM/LSAM's LOI and for the LSAM's lunar landing and departure.
That is true also in the (real) Lockheed Martin Orion (left) since its early specs talks of 15 mT for the Orion+LAS+adapter to the Ares-I 2nd stage, and, despite (so far) Lockheed Martin doesn't give any data about the Orion's SM weight, it can't be more than 10 mT (with ONLY ~7 mT of it for propellants!) since the max payload of the Ares-I is 25 mT.
The official reason given for that change (vs. Apollo) is "to send bigger cargo-LSAMs on the moon without any Orion's SM for LOI", but, despite "send a few extra-tons of cargo on the moon" may appear a good and rational choice, it has MANY (safety and operational) BAD consequences for all future moon missions!
The main problems of this (bad!) choice are about the SAFETY of the astronauts in the moon missions.
In the Apollo missions (both) the SM and LM engines/propellants was able to brake the CSM+LM to enter the lunar orbit or to fly around the moon and launch both vehicles to a safe earth-trajectory (like in the Apollo XIII contingency) while, in the new vehicles, a double-option will be IMPOSSIBLE because, if the LSAM engines will fail in the LOI, the Orion's SM will have not sufficient propellant (and thrust) to brake (both) Orion and LSAM in lunar orbit and (probably) ONLY the propellant to brake itself (if the astronauts will be FAST to undock the LSAM...) but NOT the propellant to come back to Earth!!!
Of course, the LSAMs will be built with the best reliability possible, but, all spacecrafts' accidents learn us that nothing can be sure in a space flight and the "LSAM-only LOI option" of the ESAS plan will give only HALF the astronauts' safety (or... TWICE the risk to die) of an Apollo-style "twin-way" LOI.
The second security issue may happen after the lunar surface exploration (when the LSAM docks the Orion and the astronauts must come back to Earth) if (both) the Orion's main engine and the RCS (used as "backup-engines" for TEI) don't work (maybe, for an electronic or mechanical failure).
In that will happen, the astronauts CAN be saved (since the Orion has up to 12 days of life support: 15+ days total, less 3 days for the earth-moon travel) with a second Orion (launched remote-controlled without astronauts) but they will NEVER be saved because, without the LSAM, the rescue-Orion will not have sufficient propellant for (both) LOI and TEI and will become only a big lunar orbit debris!
The only way to save the astroanuts is to launch another AresV+EDS+LSAM and an uncrewed Orion, dock them (remote-controlled) in earth orbit and send the full (rescue-Orion and expendable-LSAM) convoy towards the moon... AND ALL THAT MUST HAPPEN WITHIN EIGHT DAYS MAX !!!
But, over these BIG security problems, the (bad) "small-SM" choice will have (also) MANY operational, design and efficiency issues, some of which I explain here.
Someday (as I suggest in my Lunar Space Station article) we will have many orbital modules around the moon with very long life support (to increase the astronauts' safety, dock many cargo/crew Orion and reusable-LSAMs, multiply the lunar exploration time and quality, etc.) and these orbital module will need many crew rotations per year and tons of cargo send to/from them, but it will be IMPOSSIBLE without a bigger Service Module able to perform (both) LOI and TEI and reboost the lunar station orbit (with the extra-fuel used for LSAM-mass' LOI in a standard Orion/LSAM mission).
With a small SM we will NEVER see/have any "ApolloVIII-like" mission around the moon, no (manned or unmanned) rescue missions, no scientific orbital missions, no LSS and reusable-LSAM crew rotation, etc. ..not without launch EVERYTIME a GIANT (and VERY EXPENSIVE) AresV+bigEDS+LSAM, no matter if the LSAM will be used to land on the moon or it needs only to perform a LOI.
But the lack of lunar-orbit and earth-return mid-cargo (up to 3 mT) will be even more DRAMATIC since they must use (everytime) the giant (and very expensive) AresV/LSAM also to send a few tons to a lunar orbit module (for extra life support, science hardware, spare parts for maintenance and repair, etc.) while the ONLY earth-return cargo will be the (incredibly poor!) 220 lbs. of the Orion capsule!!!!
The planned cargo-Orion will be COMPLETELY USELESS for ISS resupply (since it can send near the same payload of a Progress at 15+ times the price) with so many (cheaper!) cargo vehicles available in 2015 (including some COTS) while it may be INCREDIBLY USEFUL to send/receive tons of cargo to and from the moon orbit or lunar surface!!!
Just imagine how much experiments and moon samples they can bring back to earth with EACH moon mission sending one crewed Orion + one reusable-LSAM + one cargo-Orion able to carry up to 3 mT of instruments and moon samples instead of the (poor) Orion's 220 lbs. only!!!
But this option will NEVER happen (surely, NOT for the cargo-return) without a Service Module able to perform (both) LOI and TEI.
The last (but not the least) problem of a small SM is the (about two times) BIGGER tanks of the LSAM's Descent Stage (since they must contain 10+ mT of extra propellant for the Orion+LSAM's lunar orbit insertion) that means LESS life support and lunar exploration hardware!
Without this tanks' extra-weight, the LSAM can land 2+ mT more lunar-hardware and TWICE the life support to have TWO+ WEEKS LONG missions instead of the (planned) one week only... it's like have "TWO MISSIONS for the price of ONE" or "ONE mission at HALF the (expected) price"!
My suggestion is to INCREASE the Orion's SM dimensions and weight to store 10+ mT extra propellant and RESIZE (the same weight) the LSAM (from 45 mT to less than 35 mT) to launch it with a smaller (120 mT payload) AresV built with two (ready available, cheper and man-rated) 4-segments SRBs.
Of course, the Ares-I must be bigger and able to lift up to 40 mT for moon missions with a smaller SM for ISS missions able to launch the Orion with a 15 mT cargo module for ISS resupply, experiments, etc. ...another "BUY FIVE - PAY ONE" since they can launch ONE crew mission and FOUR (3+ mT each) cargo missions with a SINGLE rocket!!!
September 12 - 2006
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Copyright © 2006 Gaetano Marano - All rights reserved - The base images used are © NASA and Lockheed Martin