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#1 Re: Interplanetary transportation » Reusable Rockets to Orbit » 2014-02-24 21:24:51

Hop
Rune wrote:

I know how to figure out hyperbolas since I was 17.

I've never seen the slightest evidence from either you or Josh that you can figure the speed of a hyperbola. In spite of the fact I've shown you how many times.

Hyperbolic orbits are necessary for departing earth for other planets. I will try again to teach this very simple device:

What the heck is Vinf

What about Mr. Oberth?

and

The most common delta V error

Rune plays a role in each of these.

#2 Re: Human missions » Developing the cis-Lunar economy and infrastructure » 2012-01-19 16:24:09

Hop
JoshNH4H wrote:

I think the primary point that we're looking at here is that the concentrations of metals allegedly "discovered" by the LCROSS

Josh, the alleged 1.6% gold in the LCROSS ejecta is only one of several branches this thread has split into.

#3 Re: Science, Technology, and Astronomy » Robotic Mining » 2012-01-19 16:17:15

Hop
Adaptation wrote:

Under construction is a brilliantly conceived overhead crane that manipulates large objects within a 26,896 sq ft area like a three dimensional tram.  On the moon with less gravity you can probably get it to cover much larger distances, perhaps a whole crater.  The crane could be used to run the whole mine from construction to gathering ore to loading and unloading resources from a smelter or other processing equipment.

Interesting! I'd like to check this out. If you could provide more info, I'd be grateful.

Bill Stone & crew built a robot that builds a 3-D map of it's environment. That enables it to move about without human guidance. This ability to make 3-D models of the surrounding area might enhance the power of the crane you describe.

The state of art for telerobotics devices is advancing as the cost for some of the technologies is dropping. I talk about this at Puppets, Telerobots and James Cameron.

If the performance and cost of telerobots improve as I hope, lunar exploitation becomes much more plausible.

#4 Re: Interplanetary transportation » Reusable Rockets to Orbit » 2012-01-19 16:04:12

Hop
JoshNH4H wrote:

I will also offer up the Saturn V second stage, which has enough T/W to get off the ground as well as the delta-V to make it to orbit,

I'm at a disadvantage here. I will offer links and math to back up my assertions as well as drawings to convey an idea. You as well as others just write from your gut. You proclaim the math exercises not worth your time. So you can pop out posts in 3 minutes when my posts can consume 15 minutes or 20 minutes. Time is a precious commodity for me and this lopsided exchange is annoying.

Anyway...

Saturn II C-5A

Gross mass: 384,057 kg
Dry mass: 31,740 kg
Thrust: 4446.65 kN
Specific Impulse sea level 200 s.

You can try inputting these quantities to Schilling's launch vehicle calculator

And you continue to ignore that an SSTO RLV would also have to endure re-entry. Adding TPS and other accommodations for re-entry will also harm mass fraction.

#5 Re: Martian Politics and Economy » Creating the Cis-Lunar economy » 2012-01-16 20:25:40

Hop
louis wrote:

There are lots of money-earners we haven't yet discussed.  Won't Hollywood want to start setting some of their films in part on the moon?  Who is going to provide them with the footage and backdrops?  That could generate maybe $20million a year, as would TV programmes (documentaries) about  the moon and the lunar colony.

Bill White's science fiction novel Platinum Moon explores different ways of generating revenue streams. TV rights, product endorsements, merchandising, etc.

I believe all of these should be used. I don't think this could pay for a lunar base, but it could pay for a fraction.

#6 Re: Human missions » Developing the cis-Lunar economy and infrastructure » 2012-01-16 11:00:36

Hop
Hop wrote:

3) (maybe) Constant line of sight with the earth.

I don't know the third advantage for a fact. But it seems to me a high altitude polar plateau would be a good place to erect a communications tower. It might enjoy line of sight with the earth as well as the neighboring crater basin.

I just suggested this to someone knowledgeable in the field. His response wasn't encouraging:

"As for Earth LOS comm, that's difficult due to the 5.5 degree latitude
libration -- you need about several hundred meters of tower to clear the
limb for each degree of elevation/latitude off the pole, so a tower that
encompasses all librational conditions based exactly at the pole would be
well over 2 km high.  Possible, but not in any early stage of lunar
development.  The preferred solution for initial lunar presence is a
constellation of relay satellites."

So back to Molniya relay satellites or pehaps constellations in halos about L1 or L2.

#7 Re: Human missions » Developing the cis-Lunar economy and infrastructure » 2012-01-16 10:44:15

Hop
JonClarke wrote:

If only 1/12 of the metallic asteroids remain intact, there could be substantial ore bodies on the moon.

What make you think that 12% of metallic asteroids will remain intact?

I do not know the upper limit for velocity for an asteroid to remain intact. Besides impact velocity, there are other factors: size and shape of asteroid, structural strength, impact angle, etc.

This was in response to your contention that 9% is virtually no impacts.

(oh, and by the way, you just morphed 1/12 into 12%).

JonClarke wrote:

Even if they did, what makes you think they will be ores?

Potential ores. If a lunar base whose revenues exceed operating costs is achieved, growth is inevitable. This would create economic pressure to use ISRU materials rather than supplying the base with earthly materials. Metallic asteroids have lots of nickel and iron as well PGMs.

JonClarke wrote:

2) I have never said there are no lunar mineral accumulations of potenial economic interest.  I have mentioned aluminium and titanium and of course the polar ice.  These we know about.  There may be others.

3) None of these accumulations are strictly speaking ore because they cannot be profitably mined (at present).  Ore is an economic term, not a scientific one.

In the near term I believe the ice has the greatest potential for becoming ore. Propellant high on the slopes of earth's gravity well would break the exponent in Tsiolkovsky's rocket equation. Given one export, other local resources would become attractive for a lunar base seeking to reduce costly imports from earth.

And, given reduced transportation expense, PGMs and other lunar resources might eventually be profitably sold to earth markets.

#8 Re: Interplanetary transportation » Reusable Rockets to Orbit » 2012-01-15 20:51:15

Hop
RGClark wrote:

What would be the mass ratio and delta-V if you added engines to achieve lift off?

As I mentioned to Josh, there's a trade. You can improve T/W and thus reduce gravity loss by adding more engines. But this increases your dry mass and harms mass ratio.

RGClark wrote:

BTW, Dr. John Schilling has an online payload estimator that allows you to estimate the
the payload you can lift to orbit with a launch vehicle. You enter in the propellant and dry
mass and the vacuum thrust and vacuum Isp. The program does give a warning if your
thrust is less than your launch weight.

Launch Vehicle Performance Calculator.
http://www.silverbirdastronautics.com/LVperform.html

Bob Clark

Yes, a good resource. I've linked to Schilling's calculator several times in this thread. As you mentioned it warns you if your T/W is less than one.

Schilling also posted some explanation of his calculator: Launch Methodology

He talks about the benefit of higher thrust during early ascent. He writes, in part "If dissimilar staging is allowed, the optimal design is generally one which uses a high-thrust first stage (often augmented by strap-on boosters) to rapidly escape the early high-loss flight regime, and a relatively low thrust but high Isp upper stage to most efficiently add delta-V once most loss terms have become irrelevant."

That is why I like two or even three stages to orbit. The lower stage can be high thrust kerosene to get out of the early high loss regime faster. Then the upper stages that don't need high T/W ratios can use better ISP stages. Besides having better ISP, the upper stage can have fewer rocket engines, thus helping with the mass ratio.

The major obstacle for reusing the upper stages is getting past the 8 km/s re-entry. As I mentioned earlier, propellant in LEO could provide a means for upper stages to shed re-entry velocity and thus avoid the temperature and stress of 8 km/s re-entry.

Another possibility is momentum exchange tethers.

LEOTether.jpg

The tether foot in the above illustration moves 6.9 km/s at 300 km altitude. Shaving 1 km/s not only helps with the mass fraction but lessens the re-entry abuse.

#9 Re: Human missions » Developing the cis-Lunar economy and infrastructure » 2012-01-15 20:06:18

Hop
Grypd wrote:

You are forgetting that one of the advantages of the Moon is that it is tidal locked it always shows the same face to Earth and a transmitter placed on top of the right hill will face in the direction of Earth. There is no need for a satelite communication system at first. Well not in the Moons orbit anyway there is nothing to stop these communication dishes aiming for satelites in the Earths orbit.

Indeed. People tend to forget earth is a moon synchronous satellite. It's not completely stationary as viewed from the moon's surface, it traces an analemma, but close enough.

The most interesting locations are plateaus that enjoy nearly constant illumination neighboring a volatile rich cold trap. I believe there are two such locations we know about.

The plateaus of nearly constant illumination have several advantages:

1) Mild temperature swings: -50 degrees C plus or minus 10 degrees
2) Constant solar energy
3) (maybe) Constant line of sight with the earth.

I don't know the third advantage for a fact. But it seems to me a high altitude polar plateau would be a good place to erect a communications tower. It might enjoy line of sight with the earth as well as the neighboring crater basin.

#10 Re: Interplanetary transportation » Reusable Rockets to Orbit » 2012-01-15 19:49:50

Hop
JoshNH4H wrote:
Hop wrote:
JoshNH4H wrote:

I was talking about Mass Ratio and nothing else.

You were talking about mass ratio to function as a SSTO vehicle.

If your T/W is low, you will incur excessive gravity loss and your needed delta V will be higher than 9.4 km/s.

So no, the Centaur IV does not have the mass ratio to function as a SSTO vehicle.

I believe my meaning was excessively clear and not arguable,

Mass ratio and T/W are a trade space.

For a given payload you can have better T/W by having more rocket engines, but this harms your mass ratio.

You can also improve T/W by using lower ISP but higher thrust engines. However lower ISP will also hurt your mass ratio.

Another trade space is comfort and spaciousness vs good mileage for motor vehicles. You can have the good mileage of a moped or the comfort of a limo but not both.

Saying a Centaur has the mass ratio to be a SSTO is like like saying a limo get 90 miles to a gallon. A limo doesn't get a moped's mileage. And with a very poor thrust to weight ratio, a Centaur's delta V budget for reaching LEO will not be 9.4 km/s.

The notion that a Centaur has the mass ratio to be an SSTO is not only arguable, it's flat out wrong.

#11 Re: Human missions » Developing the cis-Lunar economy and infrastructure » 2012-01-15 19:30:55

Hop
Rune wrote:

Carbon fiber rods work at +100ºC? Really? Because that is news to me. In that case, they should have no problem with the -150ºC of nighttime.

The most interesting sites are those that have volatile rich cold traps neighboring plateaus that enjoy nearly constant illumination.

The temperature swings at these polar plateaus are much milder than the lower lunar latitudes: -50 degrees C plus or minus 10 degrees.

See New Light on the Lunar Poles

#12 Re: Human missions » Developing the cis-Lunar economy and infrastructure » 2012-01-14 12:47:38

Hop
JonClarke wrote:
Hop wrote:

No, we don't.

I don't agree 9% = virtually no impacts.

Depends on your perspective.  If you are flying airliners 9% failure is an appallingly large number.

If you are a retailer who benefits from holiday shopping, December isn't an inconsequential month. And December is only 1/12 (8.33%) of the year.

If only 1/12 of the metallic asteroids remain intact, there could be substantial ore bodies on the moon.

JonClarke wrote:

If you are testing geophysical models 9% is an unbelievably small number.

The small number of Apollo samples is a lot less than 9%. Yet from these vanishingly minute data points you seem convinced there are no lunar ore bodies.

#13 Re: Human missions » Developing the cis-Lunar economy and infrastructure » 2012-01-12 10:24:57

Hop
JonClarke wrote:

We have data from more than 130 km of  lunar traverses on foot, by robot, and in vehicles.  Not one meteorite was found.  Compare with the number found on Mars over much shorter distances.  That is the difference an atmosphere makes to meteorite preservation.

Given a small meteorite with a big ballistic coefficient, terminal velocity can be quite low. A very slow impact can leave an intact meteorite sitting on the surface.

I believe any intact meteorites on the moon would be buried beneath a crater basin.

That we haven't found any intact meteorites sitting on the ground certainly does not demonstrate there aren't any intact meteorites.

#14 Re: Human missions » Developing the cis-Lunar economy and infrastructure » 2012-01-12 10:11:41

Hop
JonClarke wrote:
Hop wrote:

Velocity of a hyperbola is sqrt(Vesc^2 + Vinf^2). For most asteroids, Vinf is quite high and this is the quantity that dominates. But there are are number of asteroids with low Vinf, some have a Vinf of nearly zero. Hence I said lunar impacts can be as slow as 2.4 km/s. Which is entirely correct.

Somehow you have morphed this into slow impacts are the norm, a position I've never taken.

In that case we agree.

No, we don't.

I don't agree 9% = virtually no impacts.

#15 Re: Martian Politics and Economy » Creating the Cis-Lunar economy » 2012-01-10 12:40:42

Hop
Rune wrote:

You can smile smugly

I grow weary of your personal attacks.

#16 Re: Martian Politics and Economy » Creating the Cis-Lunar economy » 2012-01-10 11:16:17

Hop
Rune wrote:

If so, consider the trade with a single station in L1, in terms of launch windows. Something like once every two weeks from a particular orbital plane in LEO to a particular orbital plane on the moon, IIRC? No idea off the top of my head, really, but I do know L1 is accessible once every orbit, which is 90-something minutes in LEO, or pretty much anytime in other words (once a day from the ground).

If a LEO is coplanar with the moon's orbit, A Hohmann window opens about every 90 minutes.

However a LEO coplanar with the moon's orbit will not remain so. The earth's influence will see to that.

Given a LEO orbit that is inclined wrt moon's orbit, you want to launch when the space craft crosses the line of nodes (the intersection of the low earth orbit plane with the lunar orbit plane). Else you pay a delta V penalty.

A Hohmann launch window opens at a line of nodes about every two weeks. So a launch window from a given LEO opens about every two weeks. This is true of the moon, EML1, EML1 and LLO.

#17 Re: Martian Politics and Economy » Creating the Cis-Lunar economy » 2012-01-10 11:04:24

Hop
Terraformer wrote:

To get a rough Lunar base that can expand (i.e. build habitats, basic equipment etc) using predominantly in-situ resources will cost around $5 billion - possibly higher, but probably not lower. This is an upfront capital cost which will need to be paid back, say over a period of 10 years, so we need to make $500 million/year to cover this cost.

Lunar propellant mines is my favorite daydream. So it pains me to rain on my own parade.

5 billion to establish a base is very optimistic. The two architectures I find most credible are the ULA and Spudis architectures. Both those call for around 80 billion over ten to fifteen years if memory serves.

If SpaceX lowers launch costs it will mitigate expense some. However, in the early stages, a large part of the expense will be the payloads. The research and design expense will be amortized over time if you build numerous units for lunar mining, power, etc., but initially the units will be quite expensive.

Also, I don't Musk even odds for achieving TSTO RLV.

I don't thinking recouping the costs of a lunar base in a short time frame is doable.

A goal that is perhaps doable: Establishing a lunar base whose revenues meet or exceed operating expense. Once you have a base whose revenues exceed operating expenses,  growth is inevitable.

#18 Re: Interplanetary transportation » Reusable Rockets to Orbit » 2012-01-10 10:41:42

Hop
JoshNH4H wrote:

I was talking about Mass Ratio and nothing else.

You were talking about mass ratio to function as a SSTO vehicle.

If your T/W is low, you will incur excessive gravity loss and your needed delta V will be higher than 9.4 km/s.

So no, the Centaur IV does not have the mass ratio to function as a SSTO vehicle.

#19 Re: Interplanetary transportation » Reusable Rockets to Orbit » 2012-01-10 07:55:18

Hop
JoshNH4H wrote:

It is my understanding that several off-the-shelf rocket stages have the mass ratio to function as SSTO launch vehicles.  At the very least I can point to the Centaur upper stage as having this theoretical capability, seeing as I've actually done the calculations for it, though this is saying nothing of thrusting capabilities).

Doing my own calculations...

Centaur V1
Gross mass: 22825 kg
Empty mass: 2026 kg
ISP: 451 seconds

Given that ISP and mass ratio, you have a delta V of 11.15 km/s. More than enough to achieve LEO, right?

But let's look at thrust to weight ratio.
Thrust: 99190 newtons.
The initial thrust to mass ratio is 99190 newtons/22825 kg. Or 4.35 newtons per kilogram. Gravity exerts a force of 9.8 newtons per kilogram.

T/W < 1.

This stage would not even get off the ground.

#20 Re: Human missions » Mars Direct 2007 » 2012-01-07 13:36:33

Hop
Mark Friedenbach wrote:

Mars Direct is simpler, safer, and easier to pull off than DRM 3.0. The DRM was in response to MD, but added the complexity of a transfer vehicle left in Mars orbit. IIRC Zubrin spends a section in the Case for Mars discussing the problems of this approach that I won't reiterate here, but another big one that Rune didn't mention is the lack of artificial gravity on the way out. One can only speculate as to why.

It's all moot though as they way this works is that every few years some engineers working under political pressure at JSC come up with a reference mission, and then anyone within the agency or government has to use this mission as the bible for what a minimum human-to-Mars programme would look like. The current DRM is unpublished Constellation-era framework that called for multiple (!!) Ares V launches per mission, with some crazy number like 300-400 tonnes to LEO, and all for just a few weeks at a single spot on the surface. Unfortunately it's unpublished (unfinished?), but of course being the JSC-approved reference mission, it was taken at face value the only design considered by the Augustine commission, who of course said it was ridiculously expensive and put Mars off the table for the foreseeable future.

For reference, here is one flavor of Mars Semi-Direct: A Practical Architecture for Exploration-Focused Manned Mars Missions Using Chemical Propulsion, Solar Power Generation and In-Situ Resource Utilisation by Willson and Clarke

The author Clarke I believe is the same Jon Clarke participating in this thread.

---

A few notes on the Mars Semi-Direct in Willson & Clarke's pdf:

694 tonnes to LEO (on the page labeled 202)

ERV propellant isn't deep cryogenic nor is the ERV NTR. The itemized mass list includes 44.22 tonnes of liquid oxygen and liquid methane (on the page labeled 200).

Lifting an ERV off Mars' surface and sending on a Trans Earth Injection (TEI) is very challenging. To crack enough propellant, you'd need a very robust plant and power source. ISRU to provide enough propellant to get an MAV to Mars orbit is more doable. In this regard, I regard Mars Semi-Direct more plausible than Mars Direct.

Willson & Clarke have under-estimated the delta V to get from low Mars orbit to Phobos. Thus their mission plan has insufficient propellant to make their side trip to Phobos and achieve TEI. Their plan would kill the astronauts. However if they cut out the side trip to Phobos, their propellant is sufficient.

There is some controversy on the radiation shielding need to protect against GCR (galactic cosmic rays). In my opinion Willson and Clarke's radiation shielding is insufficient.

---

I haven't seen an itemized mass list of Mars Direct payloads as Willson and Clarke have done for Mars semi-direct. Given that propellant for the return trip would be from Mars, you can take 40 tonnes off the MTV as well as the ERV. But  the ERV and MTV are two separate vehicles. The MTV and hab would be the same payload in MD. I would think you'd need to land a cargo vehicle just as W & C call for in MSD. And you'd need to have Trans Mars Stages (TMS) to send the MTV, ERV and cargo vehicles on their ways.

So I believe MD would also require multiple Ares V launches (or multiple SLS launches, since Constellation bit the dust).

Valeri Polyakov demonstrated 8 months of weightlessness isn't a show stopper. So I don't regard MSD sans bolo MTV as a major flaw.

#21 Re: Martian Politics and Economy » Mars Economic Activity » 2012-01-07 11:11:07

Hop
JoshNH4H wrote:

Providing evidence for claims is a vital part of academic argument.

Very true. However in this regard you're in no position to criticize Louis.

#22 Re: Interplanetary transportation » Reusable Rockets to Orbit » 2012-01-07 11:05:30

Hop
JoshNH4H wrote:

It's difficult, though certainly not impossible, to get your mass ratio down to that area anyway

The mass ratio is only part of what I said. You need a large ratio and having a spacecraft strong and temperature resistant enough to endure re-entry.

Whether that's possible, I don't know. It has yet to be demonstrated.

JoshNH4H wrote:

At the very least I can point to the Centaur upper stage as having this theoretical capability, seeing as I've actually done the calculations for it, though this is saying nothing of thrusting capabilities).

Needless to say, I don't regard your math as consistently sound. I would need to see a cite and the work behind your calculations.

#23 Re: Human missions » Mars Direct 2007 » 2012-01-06 14:36:40

Hop
JoshNH4H wrote:

While the most specific technology proposals of Mars Direct may have been superseded, I don't think it's correct to say that the idea of ISRU fuel production (the primary technical difference between Mars Direct and Mars Semi-Direct) is still very much a valid concepts.

The Mars Semi-Direct plans I've seen call for ISRU fuel.

#24 Re: Martian Politics and Economy » Mars Economic Activity » 2012-01-06 14:29:21

Hop
Mark Friedenbach wrote:

No, I mean how do you figure you could clear 5,000 watches per year, and how did you figure that availability would effect its actual price?

The Apollo/Soviet samples were being sold on the open market, to collectors at the going rate of lunar material. It's entirely relevant.

I been over this a 100 times with Louis. Supply and Demand. Once rare objects becoming abundant. A niche market spending millions suddenly becoming wealthy enough to spend many billions.

He is deaf to all these arguments.

#25 Re: Interplanetary transportation » Reusable Rockets to Orbit » 2012-01-06 14:24:00

Hop
GW Johnson wrote:

Paper airplanes from ISS.  Interesting.  The ultimate in low wing loading.  Did they ever run this experiment?  Especially since the ignition point for paper in air is about 451 F or 233 C? (not as exciting in metric,  thanks to Ray Bradbury).

The 8 km/s re-entry is a major problem. They have a thread on RLVs at NasaSpaceFlightForum. Danny Dot noted the difficulty of finding durable materials that can withstand the temperature. He said the shuttle's leading edge was 3000 degrees F. He complained of a TPS material being softer than chalk.

It seems to me one of the problems is achieving an FMR of 16:1 and having a spacecraft strong and temperature resistant enough to endure re-entry.

Watching Musk's Grasshopper video it looks like he hopes to use reaction mass to shed re-entry velocity in addition to aerobraking. If he hopes to achieve some re-entry delta V with propellant, this makes his FMR even more challenging. Get the FMR too high and you have a very tenuous, fragile vehicle even less able to endure re-entry. I'm not giving Musk's TSTO RLV even odds.

However, given propellant in orbit, I believe it's quite doable to decelerate the upper stage and land it intact on the launch pad. Thus I believe lunar supplied propellant depots would enable TSTO RLVs.

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