Hypography X Prize Entry

[Pyrotex]

Originally Posted by Turtle

...PS Had to look up "RCS", and still can't find what it's an acronym for, but found we can have engines custom made? ...

RCS = Reaction Control System

An RCS is used for two purposes: 1. to control the attitude (pointing) of the spacecraft. 2. to make small changes in the crafts' speed (delta V) so that it arrives on target.

An RCS is made up numerous small rocket nozzles which point so that each one will cause the spacecraft to spin (rotate) in a particular direction. For some spacecraft, these nozzles are truly tiny, with propulsive forces measured in ounces.

There are vendors who will supply RCS components and ready-to-mount systems in the proper size.

[Pyrotex]

From the lack of responses, I'd say this was all pretty daunting. It gets worse.

ROCKET SCIENCE LESSON #2

You got to do a risk analysis with a "fault tree" on every component of the Lunar Payload, including the Rover. This starts with a diagram of every every "box" or replaceable unit (RU) and how they are connected by data cables, power cables, mechanical links, etc. For each RU, a table is created showing each failure possible and how that failure spreads to other, connected RUs. Consider falling dominos. Consider the poem "for want of a nail, the shoe was lost, for want of a shoe, a horse was lost...".

Why, for pity sake?!?! Assume that each RU is 99% reliable, and you have 100 RUs with no redundancy. What is the probability that the collection of RUs will work as planned. Less than 37%. that's 0.99 to the power of 100. About 1 chance in 3. Not good enough.

You can address this with redundancy. You can address this by making each component RU MORE reliable. At 99.5% reliability, the same 100 RUs now have a 60% chance of success.

[Jay-qu]

Yes it is daunting, but thats part of it that makes it so exciting!

[CraigD]

Originally Posted by Pyrotex

From the lack of responses, I'd say this was all pretty daunting.

I, for one, admit to being daunted. A lunar X challenge is much harder to start than, say, a front porch tear-out/design/rebuild, and even this minor project is capable of daunting me! A certain “put up or shut up” factor is involved here, too, I think – it’s easy to propose spaceflight systems when there’s little possibility of actually implementing them in the near future, but to win google’s tens of millions (and science hobbyist near godhood), the team actually has to build this thing, and land it on the moon. I can’t shake the feeling that this would ultimately entail some pretty major commitments – dayjobs quit, personal property liquidated, etc. – taking the participant out of the domain of hobbyist into that of professional space engineer/scientist (best case) or the sad sort of person newpapers and local TV newsrooms run human-interest features on on a slow news day.

Originally Posted by Pyrotex

You got to do a risk analysis with a "fault tree" on every component of the Lunar Payload, including the Rover. …

True, but I think we’re still in the idea/brainstorming phase, with at least one major phase – unit/integration testing (in which, if all goes according to (my vaguely envisioned) plan, some lucky person, maybe me, get to play with RC vehicles in a big vacuum chamber) – before we get to risk/failure mode analysis.

So here’s some idea/brainstorming:

Looking at the project as a whole, I see something like this:

• Launch – Using a commercial system, so a non-issue/someone else’s problem
• Propulsion – I’m pretty sure hydrazine thruster(s) of whatever size the design requires can be fabricated, and, due to their simplicity and proven record, are 99.99+ % reliable.
• Landing – Been done with much more primitive hardware. 1/6 g in vacuum is a forgiving flight domain. I’m not sweating this.
• Rover operation – Fancy RC cars with video cameras. No sweat here, either
• Communication – It’s a long way to the moon. This, I’m sweating significantly.
• Navigation/guidance – Historically (eg: the 1960s’ Luna program), navigation failure accounts for more failures than anything but launch failures. Determining the position and velocity of unmanned vehicle – essential to getting it to a specific desired position and velocity (ie: stationary on the moon’s surface) – is critical.

Lots to talk about. I want to brainstorm about navigation.

The traditional navigation system on a moon flyby/orbit/lander determines position by getting optical fixes on points on the earth, sun, stars, and planets. I wonder, could we do better now, using the GPS, or other radio range and direction systems?

The GPS is intended to provide precise positions near the Earth’s surface. However, weak radio signals, including the timing information necessary for the system to work, are, I suspect, transmitted into space. Could a sensitive receiver on our spacecraft use these stray signals to get position fixes more accurately than a traditional navigation system? If so, it seems such a system would be simpler, cheaper, and more reliable than the traditional ones.

Alternately, could a special ground-based system be used? This would involve having enough ground transmitters to always have a “constellation” of 3 or more widely separated transmitters within effective line of sight of the spacecraft. Vs. existing GPS, it has the disadvantage of having to be built, atmosphere and weather issues, and the advantage of being made as powerful as necessary, reducing the required sensitivity of the spacecraft’s receiver.

Alternately, could the spacecraft be the transmitter, and several ground stations the receivers?

The key to a radio positioning system like GPS is a precisely timed transmission coupled with a very accurate clock. In commercial near-Earth’s surface, is accomplished with a good crystal clock that sets itself from the satellites’ atomic clocks. A more expensive system could have its own atomic clocks.

I suspect that at least one of these options is a significant improvement on a more traditional guidance system. In essence, they take advantage of our current technological ability to make such precise timings that we can determine transmitter-to-receiver distance down with great precision by measuring the travel time of the signal.

Of these options, the first, using the existing GPS satellites, is most attractive to me, because it could be very inexpensive.

[Mercedes Benzene]

I'm getting excited now.


I'd like to focus primarily on propulsion if that's okay...
Doing some research, it seems that most of the work can be done for us with preconstructed systems. Here's one website that I found interesting:

Monopropellant Hydrazine Thrusters

It seems lots of companies have systems that can be made to order, and will then be ready to assemble.

[silverslith]

A big limitation is obviosly the need for hardened electronics. This could be avoided if a sensible earth-moon vehicle is used. putting the goods inside a snowball of frozen fuel is the answer for getting any microelectronics through the rad belts. over 50 tons of shielding is needed otherwise. If you use your fuel as the shielding then no probs. Daytime moon is still a bit messy tho.

[Pyrotex]

And so, we come to (you knew this was coming)...

ROCKET SCIENCE LESSON #3

Once you have the outline of your WBS (it needn't be complete), then you must start your design with the most important things: REQUIREMENTS.

Generically, a requirement (or "reqt") is just a statement of something your design must provide, accomplish, or withstand. There are three levels of requirements:

1. Mission Reqts. What must the overall mission provide, accomplish, fulfill, etc.
For example:
1.a. The mission shall place a remotely controlled rover on the surface of the Moon.
1.b The mission shall be accomplished by November 15, 2012.
1.c The mission shall cost no more than US$ 95,000,000.

2. System Reqts What each major system must provide, accomplish, fulfill, withstand, etc.
For example:
2.a The lunar rover system shall weigh no more than 5.7 kg.
2.b. The lunar rover shall function for at least 12 days.
2.c. The lunar rover shall travel at least one kilometer in its lifespan.
2.d. The lunar rover shall return full visible spectrum digital photographs of 3 megapixels each; at a maximum rate of 10 photographs per second.

3. Component Reqts. What each component must provide, accomplish, fulfill, etc.
For example:
3.a. The rover motor assemblies (including electronics) shall operate within the temperature range of -10C to 100C for a minimum of 90 days.
3.b The motor assemblies shall operate in a Lunar radiation environment for a minimum of 90 days.
3.c The motor assemblies shall operate in vaccuum for a minimum of 90 days.

If we were to be as exhaustive as NASA is, our payload section, with landing system and rover, would require about 6 shelf feet of reqts documentation. We can probably get by with a dozen 1-inch 3-ring binders.

Why reqts? Because they drive design. Somebody designs a wonderful motor assembly capable of driving the rover at 10 mph. But wait, the system reqts only demand 1.5 mph. That motor is over designed, and probably weighs too much and certainly takes too much electrical current. It's out of spec. But isn't 10 mph better than 1.5 mph? Not necessarily. What if the wheel and axle design can't support 10 mph? What if the batteries aren't big enough to go that fast. And besides--everybody agreed to 1.5 mph! Your fancy shmancy motors have bollixed up everybody else's design and threatens to sabotage the project. Sorry, but it's true.

Agreeing on reqts keeps everybody designing toward the same consistent vision. It keeps weight down, minimizes resource demands, avoids technological risk, promotes success.

Of course, the down side is, that means you'll find "the perfect" RC buggie that will carry a big camera with zoom, and it puts the whole payload way over the agreed upon mass limit for the rocket. Damn. Reqts keep enthusiatic, but narrowly focused engineers from forcing everybody else to redesign THEIR systems.

[Pyrotex]

Originally Posted by CraigD

I, for one, admit to being daunted. ...Of these options, the first, using the existing GPS satellites, is most attractive to me, because it could be very inexpensive.

I have talked to a couple of **real** rocket scientists and they are very doubtful that GPS could be used at the Moon. GPS use reflector antennas to put 95%+ of their transmission on the surface of the Earth. From an altitude of about 500 miles. (more or less) At 125,000 miles, the surface of the Moon is 250 times further away. So any GPS radio power that "leaked" in the Moon's direction would be diminished by another factor of 62,500!

Sorry, but that idea, though brilliantly creative, prolly won't work.

[Pyrotex]

ROCKET SCIENCE LESSON #4

"Where to Start"

Brainstorm the overall concept of the project until you can write down the basic mission requirements. Probably 1 or 2 pages.

Make a list of the top 10 "tasks" the mission must accomplish. Like: get to the Moon; slow down; navigate to right place; land; activate rover; etc. Come to an agreement in principle as to how each of these "tasks" shall be done. For example, "navigate" could be done either from the ground or autonomously with a star-tracker.

Complete the top level of the Work Breakdown Structure (WBS) to at least the system level, and to sub-system level if it's easy. Probably 1 or 2 pages.

Take first crack at defining the reqts for the systems in the WBS. Probably 1 or 2 pages per system.

Break each system down into sub-systems as necessary; and sub-systems down into components as necessary.

Make pretty drawings of each system. Demonstrate with the drawings how each system is going to fullfil its share of the mission reqts; and its system reqts.

Complete the system reqts. Draft the sub-system reqts. About 1 page per sub-system.

For each system and its sub-systems, start a list of all the potential failures. For example: motor switch fails OFF; battery overheats; rover falls over; etc. Discuss possible failures, their likliehood, and what can be done to avoid or overcome them. For example: supply redundant motor switches; provide passive cooling to battery with radiators; supply motor override shutoff via a tilt-meter. About 2 or 3 pages per sub-system.

Design each system with as much detail as you can. Estimate mass and volume. Add up all masses and volumes to verify you still meet mission reqts.

Etc. Etc. Etc.

[Turtle]

Originally Posted by Pyrotex

I have talked to a couple of **real** rocket scientists and they are very doubtful that GPS could be used at the Moon. GPS use reflector antennas to put 95%+ of their transmission on the surface of the Earth. From an altitude of about 500 miles. (more or less) At 125,000 miles, the surface of the Moon is 250 times further away. So any GPS radio power that "leaked" in the Moon's direction would be diminished by another factor of 62,500!

Sorry, but that idea, though brilliantly creative, prolly won't work.

I agree the GPS is doubtful for Moon use. A couple corrections: the Moon is 250,000 miles away and the GPS satellites orbit at ~12,600 miles above Earth. This source says they use only a 27 watt transmitter...High Sensitivity GPS - Wikipedia, the free encyclopedia

In order to receive our signal, do we have to contract with existing radio receivers?

That is all.