The LM maneuvres pre docking

[Allan F]

Thank you. My first attempt gave _{0.25 K}

[Mag40]

Thanks Ka9Q! The signals to fire the thrusters....do they involve fixed amount of fuel, or is it astronaut skill?

I know this is an old thread, but I just noticed you asked a question that I never answered.

The RCS thrusters had constant thrust -- 100 lbf each. Impulse was controlled by how long you held the propellant valves open. You could also effectively vary thrust by rapidly cycling them with a particular duty cycle. But because the valves are electromechanical, and because it takes finite time for the propellants to mix, ignite and build thrust, there is a practical "minimum impulse" for each firing. The computer took this into account when computing which thrusters to fire, when and for how long. This is one of the main reasons for "dead bands", an allowable margin of attitude error within which the computer would not try to correct the error further.

The computer could be instructed to maintain a given attitude within the dead band, which it would do as efficiently as possible, or an astronaut could fire them manually in which case fuel consumption depended on his skill. Transposition and docking was performed manually shortly after TLI, and the CMPs seemed to compete with each other for bragging rights as to who could do it with the least amount of gas.

Thanks again. One of the more interesting upshots of this thread, is finding out that the film speed is not accurate, due to the way it is rendered into digital from 6fps.

I wonder whether there is a site out there that allows interactive docking just like the Lunar Module landing simulator online.

[JayUtah]

I wonder whether there is a site out there that allows interactive docking just like the Lunar Module landing simulator online.

Not exactly online, but some of the Apollo add-ons to Orbiter do this.

[VQ]

I wonder whether there is a site out there that allows interactive docking just like the Lunar Module landing simulator online.

Not exactly online, but some of the Apollo add-ons to Orbiter do this.

Second that. I spent waay too much time with http://nassp.sourceforge.net/wiki/Main_Page three years ago, but it looks like that project hasn't been updated since 2012. It includes a http://www.ibiblio.org/apollo/ complete AGC emulation (possibly just block 1 though), simulation of a significant portion:

of the CSM's internal electrical, thermal, and life support functions, limited failure simulations, and of course realistic fuel and acceleration constraints on all the hardware. It is a bit of a handful, though - check out the http://nassp.sourceforge.net/wiki/Apollo_7_Quickstart_-_Launch "quickstart" checklist just for getting A7 to orbit.

For a shallower learning curve, http://www.orbiterwiki.org/wiki/AMSO AMSO is more of an "interactive movie" of an Apollo mission. Much more approachable, but also less depth. It appears to have been updated significantly since 2011, so maybe the "depth" portion has improved.

[ka9q]

complete AGC emulation (possibly just block 1 though), simulation of a significant portion:

of the CSM's internal electrical, thermal, and life support functions, limited failure simulations, and of course realistic fuel and acceleration constraints on all the hardware.

Or at least pre-Apollo 14, when an emergency battery was added to the SM if the fuel cells go offline for some reason. The new battery was identical to one of the LM's descent batteries (400 Ah @ 28V) so it was nowhere near enough to run a whole mission, but it could help keep the CM's entry batteries from being depleted while a fuel cell problem is being worked.

The Skylab models had three such batteries to supply all of the power needed by the CSM from undocking to CM/SM separation, as the fuel cells were dead by the end of the mission.

I've wondered how high the energy density of a battery would have to be to be lighter than the fuel cells, their reactants, tanks and plumbing. On the other hand, an oxygen supply would still be needed for the cabin atmosphere anyway, along with a water supply. The fuel cells produced water as a byproduct, and it could be used both for drinking water and for cooling.

It depends on mission duration, but I suspect that you need solar panels to do better than fuel cells; even lithium primary batteries probably wouldn't cut it alone for more than a very short mission.

[ka9q]

How much information has NASA released about Orion? I'm particularly interested in how its power consumption and thermal load compares with the Apollo CSM. I think it could be considerably less with modern electronics.

Computers, navigation, instrumentation and communications should draw considerably less. The biggest remaining item in the communications power budget would be the RF power amplifier for the downlink and that would depend on the data rate. A lot of HDTV would drive it up.

The environmental control system (life support, cooling) should take somewhat less, as most of its power goes to pumps and blowers that have gotten only moderately more efficient since Apollo.

Lighting should also take somewhat less if LEDs replace Apollo's fluorescent lighting. OTOH, Apollo used glow-in-the-dark radioactive lighting for its switches, which is out of style today.

[VQ]

The environmental control system (life support, cooling) should take somewhat less, as most of its power goes to pumps and blowers that have gotten only moderately more efficient since Apollo.

True that basically nothing has improved as much as computers in terms of power consumption, but would a contemporary spacecraft have any need for the inverter system and 115 V AC power? As near as I can tell the primary purpose of the system was to operate fans, and modern electronically commutated fan motors would handle the "inversion" for this purpose locally and far more efficiently.

[smartcooky]

The environmental control system (life support, cooling) should take somewhat less, as most of its power goes to pumps and blowers that have gotten only moderately more efficient since Apollo.

True that basically nothing has improved as much as computers in terms of power consumption, but would a contemporary spacecraft have any need for the inverter system and 115 V AC power? As near as I can tell the primary purpose of the system was to operate fans, and modern electronically commutated fan motors would handle the "inversion" for this purpose locally and far more efficiently.

What about igniters for the ascent rocket motor. Did they have a banger-box (HEIU) like a jet engine. Most banger boxes I ever worked on was 115v 400Hz. There were 28v ones but they were quite a bit heavier.

[VQ]

The igniters on the hypergolic ascent engine? 

AFAIK, the only AC systems were on the CM. (We need more initialisms!)

[smartcooky]

The igniters on the hypergolic ascent engine? 

OK, so you are saying that there is no electrical ignition of that motor?

(Please note: What I know about the fine details as regards rocket motors can be scratched on an aspirin with a prybar.....in caps!)

[ka9q]

What about igniters for the ascent rocket motor. Did they have a banger-box (HEIU) like a jet engine. Most banger boxes I ever worked on was 115v 400Hz. There were 28v ones but they were quite a bit heavier.

I don't know what a banger-box is, but the ascent engine on the Apollo LM is hypergolic, like every rocket engine on the CSM and LM, so all you need to start it is to pressurize the propellant tanks and open the valves into the engine. No igniter needed as the propellants ignite spontaneously on contact.

Many hypergolic engine propellant valves are electrically operated with some sort of boosting. The LM ascent engine uses pressurized fuel as a hydraulic fluid to actually move the valves. I'm familiar with a MBB 400N engine in which electrically operated pilot valves gate pressurized helium to operate a second set of valves that actually let the propellants flow.

In any event, the electrical energy requirements of a spacecraft chemical propulsion system are minimal because the engines are operated for such a short time. The largest drains of the Apollo propulsion systems were probably the gimbal motors on the CSM's SPS and the LM's DPS that steered the engines in the desired direction. The SPS gimbals were started a few minutes into ascent from KSC so the SPS could be used to achieve a contingency earth orbit in case the S-IVB shut down early. They drew so much power that the CM's entry batteries had to supplement the fuel cells and be recharged later. I can't find how much power the LM DPS gimbals drew, but it's probably less than the SPS simply because the engine was smaller.

An electric spacecraft propulsion system (e.g., plasma or ion rocket) is a completely different animal; there the electrical power requirements drive the entire electrical power system design.

[ka9q]

OK, so you are saying that there is no electrical ignition of that motor?

No. The word hypergolic, by definition, means that the two propellants ignite spontaneously on contact, with no igniter (heat, spark, etc) needed.

Most hypergolic rockets use some form of hydrazine as fuel and some relative of nitric acid as the oxidizer. Their advantage isn't so much that they don't require an ignition system, but that they can be stored indefinitely as liquids at room temperature. Kerosene can, but oxygen cannot. This is important on a long space mission.

Fuels such as aniline have been used in the past, but since the mid-1960s the three most common hypergolic fuels are straight hydrazine (N₂H₄), monomethyl hydrazine, MMH (replace one of the hydrogens in hydrazine with a methyl group, CH₃), and unsymmetrical dimethyl hydrazine, UDMH (replace both hydrogens on one end with methyl groups). All are highly toxic, carcinogenic and (obviously) flammable. At least they're water soluble, unlike gasoline and other hydrocarbons, so you can flush spills with lots of water.

The big service propulsion system engine on the CSM plus all the engines on the LM used a 50-50 mixture of straight hydrazine and UDMH called Aerozine-50; the CSM RCS used MMH.

Nitric acid itself was used as a hypergolic oxidizer for a time, but since the mid 1960s the oxidizer of choice has been nitrogen tetroxide, N₂O₄, an evil-looking (and smelling), highly toxic reddish-brown gas or liquid that's one of the major components of photochemical smog. If you look at videos of the recent Proton launch failure in Russia you'll see a big reddish-brown cloud on the edges of the fireball; that's nitrogen tetroxide.

Hypergolic fuels aren't much used in launch vehicles anymore (the Proton is one of the last, and I think the North Koreans are using them) because their extreme toxicity and reactivity make them difficult and expensive to handle. Technicians loading them into spacecraft have to wear special "scape" pressure suits in case of a leak. The Apollo ASTP crew nearly died from nitrogen tetroxide poisoning during descent when some got sucked into the cabin through an open vent. It's so toxic because it forms nitric acid on contact with water, which then eats your lungs out from the inside.

NASA has sponsored development of replacement propellants for some time, and most of the promising combinations use nitrous oxide, N₂O as oxidizer. Despite being made of the same elements as nitrogen tetroxide, nitrous oxide is vastly less toxic and corrosive; in fact, it's widely used as an anesthetic. But it's usually not hypergolic, so any engines that use it will need an ignition system. Its big advantage over liquid oxygen is that, like nitrogen tetroxide, it can be stored as a liquid at room temperature but under considerably more pressure.

[smartcooky]

What about igniters for the ascent rocket motor. Did they have a banger-box (HEIU) like a jet engine. Most banger boxes I ever worked on was 115v 400Hz. There were 28v ones but they were quite a bit heavier.

I don't know what a banger-box is, but the ascent engine on the Apollo LM is hypergolic, like every rocket engine on the CSM and LM, so all you need to start it is to pressurize the propellant tanks and open the valves into the engine. No igniter needed as the propellants ignite spontaneously on contact.

Many hypergolic engine propellant valves are electrically operated with some sort of boosting. The LM ascent engine uses pressurized fuel as a hydraulic fluid to actually move the valves. I'm familiar with a MBB 400N engine in which electrically operated pilot valves gate pressurized helium to operate a second set of valves that actually let the propellants flow.

In any event, the electrical energy requirements of a spacecraft chemical propulsion system are minimal because the engines are operated for such a short time. The largest drains of the Apollo propulsion systems were probably the gimbal motors on the CSM's SPS and the LM's DPS that steered the engines in the desired direction. The SPS gimbals were started a few minutes into ascent from KSC so the SPS could be used to achieve a contingency earth orbit in case the S-IVB shut down early. They drew so much power that the CM's entry batteries had to supplement the fuel cells and be recharged later. I can't find how much power the LM DPS gimbals drew, but it's probably less than the SPS simply because the engine was smaller.

An electric spacecraft propulsion system (e.g., plasma or ion rocket) is a completely different animal; there the electrical power requirements drive the entire electrical power system design.

OK, thanks, that clear thing up

I had no idea what a hypergolic motor was let along how it works.

NOTE: Banger box is slang for a High Energy Ignition Unit. Think spark plugs for a jet engine, except MUCH more powerful. If you're ever near a jet or turboprop engine when it starts, you can hear the banger box firing away as the turbine become to wind up.

Here a small igniter being tested

The sparks are typically 15KV or greater

   

[ka9q]

AFAIK, the only AC systems were on the CM. (We need more initialisms!)

The CSM and LM both had 3-phase 115V 400Hz AC power inverters. It was used mostly to drive AC induction motors, but also to produce DC voltages higher than 28V (e.g., in the CM's entry battery charger).

There's nothing really wrong with AC per se. It's just that there's not much need for it anymore on a spacecraft. Even during Apollo the brushless DC motor was already starting to displace the conventional AC induction motor. (A brushless motor is just a 3-phase AC induction motor with its own inverter.) DC-DC converters are now efficient and lightweight, and can minimize I²R losses and wire weight when sending bulk power over lengthy wires.

28V DC was used on Apollo because it's an aviation standard since forever, but it's rather low for a large spacecraft like the ISS so the non-Russian segment standardized on 125V DC for distribution with the solar arrays operating at around 160V. The Russians still use 28V DC.

[ka9q]

Here a small igniter being tested

Ah so. Yeah, I'd say they're pretty powerful.

I don't know large rocket engines as well as spacecraft hypergolics, but I know that some that use non-hypergolic propellants (e.g., RP-1 kerosene + LOX) still used hypergolic igniters. The F-1 on the Saturn V first stage used a cartridge containing a mixture of triethylboron and triethylaluminum. This wicked stuff burns on contact with air to say nothing of LOX. Of course, this means the engine can only be started once but that traditionally hasn't been a problem in a launch vehicle.

The J-2 engine on the S-IVB (though not the S-II) had to be restartable so it did use a spark igniter. (This failed on Apollo 6.) When a spacecraft needs a parking orbit or coast period, most launch vehicles still use hypergolic upper stages to make restarts easy but I think that's starting to change. And SpaceX will restart its first stage kerosene/LOX engines so it can recover them in a soft landing.