Showing posts from August, 2010

Rock Envy

With the exception of Hayabusa, all asteroid missions to-date have been to targets bigger than 1 km in "spherical radius".

DateEncounterAsteroidRadius (km)Spacecraft1991Flyby951 Gaspra6.1Galileo1993Flyby243 Ida15.7Galileo1999Flyby9969 Braille~1Deep Space 12000Flyby2685 Masursky~8Cassini2001Landing433 Eros8.42NEAR Shoemaker2002Flyby5535 Annefrank2.4Stardust2005Sample
Return25143 Itokawa0.165Hayabusa2006Flyby132524 APL~1.1New Horizons2008Flyby2867 Šteins~2.8Rosetta2010Flyby21 Lutetia95.8Rosetta
This has led a number of people to express dismay that all the asteroids which have been identified for human exploration missions have significantly smaller estimated sizes.

DateAsteroidRadius (m)20162008 HU4~520171991 VG~4520192008 EA9~620202007 UN12~420251999 AO10~3520262008 JL24~2.520282006 RH120~2.520292000 SG344~22.5
Notice that the scale has changed from km to m. Of course, exactly why these rocks are small is most probably what makes them optimal for a human mission. Their close…

Early vs Late Human Missions To Deep Space

Anyone who has enjoyed my recreational attempts at designing a human mission to a near-Earth asteroid should check out the newly released mission to an asteroid by a team at Lockheed Martin*. The report ends with these important words:

The Plymouth Rock study shows that the first visits to asteroids can be easier and earlier than we have previously thought. The United States does not need to wait for more advanced technologies or develop expensive dedicated deep space vehicles. We can explore the asteroids within a decade, using spacecraft already being developed and tested.
This is a reasonable statement which I agree with. As far back as Apollo the question of "are we ready?" has been asked, and despite the success of Apollo it is still being asked. I have tried to make the argument that a Dragon capsule would be sufficient for a bare-bones mission to an asteroid, assuming some modifications to life support systems, dual use of propellant and supplies as radiation shiel…

Smacking Asteroids For Resources

Video by Eric Brueton

Summer studies of space settlements by Gerard O'Neill and NASA in the 70s and again in the early 90s both determined that significant amounts of mass is required for passive radiation shielding. Although structurally, most designs call for refined steel, it has been suggested that mass for the shielding could just be raw lunar regolith, left-over slag from future on-orbit industrial processing, or obtained from the asteroids. The asteroids are seen as preferable as, in terms of delta-v, they are most easily available. The typical argument is that a long duration mission to rendezvous with a near-Earth asteroid or comet (collectively, near earth objects, or NEOs) could skip a lot of launches from deep gravity wells, either digging into the NEO or
dismantling and processing it to make a nearby structure, or both.

The wrinkle, however, is in that "long duration" part. In terms of delta-v, there are NEOs which are easier to hit than the Moon, but al…

Prospector's Skymap

There have been over 535,000 asteroids discovered to date and they're all different. Some 7,121 of them are known to cross the orbit of the Earth and so are referred to as the near-Earth asteroids. If you're interested in flying a robotic mission to an asteroid, you need some idea of how much delta-v your spacecraft is going to need. I've written on this before. However, if you're interested in flying humans to an asteroid, you also need to know how long the round trip is likely to be.To answer this, one needs to know both how far away the asteroid is at closest approach to Earth, and for how many days it will remain that close. To the interested public, finding this information out using the available NASA tools is a slow process, and understanding what you've discovered is difficult without good visualization. Introducing the Prospector's Skymap, a tool for visualizing Earth-centric plots of asteroid trajectories over the next 20 years, in 3d. Included i…

Mission To Asteroid Using SpaceX Hardware - NASA's Target

As a target of study, NASA has identified the asteroid 1999AO10 as the 2025 destination for human exploration. We've heard that NASA plans to build a giant heavy lift vehicle to make the trip, but is it really necessary?

I previously described a human asteroid mission, but I assumed the logical choice of asteroid with the lowest known delta-v (and included analysis for the second lowest too), but for some reason this isn't as interesting to NASA, so let's consider how one might do the trip to their preferred target, using existing SpaceX hardware.

The reference numbers are: Earth departure stage 3291m/s, and storable propellant 3939m/s of total delta-v. We could improve this by carefully measuring the boiloff of LOX in Falcon 9 upper stages and analyzing the required insulation to do the arrival rendezvous using non-storable propellants, but I don't really have that information handy, so I'll just go with the storables.

Like last time, we'll use the Dragon …

The Asteroid Menace

Day one of the Exploration of Near Earth Objects Objectives Workshop saw the presentation of three key reasons to send humans to visit asteroids: science, mining and planetary protection. Of these, the last has has been shown to be an issue that attracts mainstream support, no doubt we have Bruce Willis to thank for this.

The workshop began with presentations of the robotic missions that have been flown to asteroids and comets. The recently returned sample return mission Hayabusa, taking pride of place. All the presenters had war stories of the operational difficulty of flying to these objects, and some expressed surprise that their missions succeeded at all. They also talked about the high cost of these missions in terms of remote sensing equipment and the lack of good ground truth information to calibrate these instruments.

Unsurprisingly then, they all support a human mission to an asteroid or a comet near Earth to more efficiently gain scientific results. However, when aske…

Deep Fried Astronauts

Back in 1967 the Bellcomm put together a study for the then Manned now Marshall Spaceflight Center. The mission was a one year human flyby of Venus. The study included some innovative stuff, like using the Earth departure stage tanks as a living module after venting any remaining fuel into space, but it also contains a fair bit of misinformation about radiation exposure, advocating that no attempt be made to shield against galactic cosmic radiation. This is to be expected.

What isn't expected is that this is still the general consensus today, even though a more recent computational study has provided some interesting numbers for various shielding materials.

Shield Material (5g/cm^2)Annual radiation dose (mSv*)Aluminum542Polyethylene450Iron581* Quality factor recommended in ICRP-60 is assumed.

This looks pretty good when the astronaut lifetime radiation limits are considered.

Astronaut ageCareer effective dose limits
(mSv, average life loss)MalesFemales25520, 15.7370, 15.930620, 1…

Throwing Stuff In Space

In my last post about the Russian space program I said that cosmonauts regularly throw stuff in space so it will burn up and not result in permanent space junk. A reader asks whether you can actually do this.. Man, way to ask a hard question.

Orbital mechanics says "if a space vehicle comes within 120 to 160 km of the Earth's surface, atmospheric drag will bring it down in a few days, with final disintegration occurring at an altitude of about 80 km", and we can work out how much delta-v a cosmonaut has to impart to get the semi-major axis of the orbit of the debris below 160 km.
dVA = sqrt(GM*(2.0/rA - 1.0/((rA + rB) / 2.0))) - sqrt(GM/rA)
where rB = 160km + roEwhere rA = 278km + roE to 460km + roEwhere roE = 6378.1kmwhere GM = 6.67300 * 5.9742 * 10^24 * 10^-11
with the ISS at 278km the delta-v retrograde is 34.684365m/s or 77.5867148 mph, which is major league baseball.with the ISS at 428km the delta-v retrograde is 77.243278m/s or 172.788292 mph, with is space cannon t…

A Disappointing End To The Russian Space Station Program

Thankfully no-one really cares about the Russian space program, or, ya know, they don't speak English, I guess. Everyone has heard of Mir but name any prior station. Go on, name one. Ok, that's easy, but how many space stations did the Russians have before Mir? I'll get back to you on that.

So what was the point of all these stations? We all know the reason why the US has the ISS, and anyone who watched the Augustine committee proceedings last year heard about why the "international community" is demanding it be extended until 2020 and beyond. Scientific research or something right? The 2005 NASA Authorization Act designated the ISS as a national laboratory. Oh sorry, the American segment of the ISS, because obviously the US can't designate the Russian segment as a national laboratory of the US, but that's what it is right? Well, no.

The Russians do very little scientific research on the ISS. They have only "mini-racks" on the Poisk mo…

Nuclear Rockets In The Atmosphere?

In James Dewar's latest book he proposes the development of a new solid core highly enriched uranium rocket engine based on the B-4 core developed in the Rover/NERVA program, but unlike that program he recommends starting small, testing in a dedicated exhaust processing facility and building successive generations of engine to prove safety and gain operational experience.

The first engine to be put into operation would have 40,000lbf (800MW), an ISP of 1,000s and weigh 6,000lb. It would have a maximum burn time of 15 minutes. The gross mass for the stage would be 91,000lb with 45,000lb of LH2 fuel, and a 3,000lb cocoon to recover the engine, to deliver a 17,000lb payload to LEO*. The stage would be dropped from 50,000ft by a cargo plane (such as the C-5A), and solid rocket boosters would carry it to 100,000ft before the solid core engine engages. The deorbited engine in its cocoon would be recovered from a splashdown for processing, as the U-235 would only be ~1% spent in the s…

Scaled Composites' Dirty Little Secret

The public is incredibly easy to fool. Way back in 2004, Mike Melvill made history by flying Burt Rutan's beautiful creation SpaceShipOne across the unofficial border to space, twice, and later that year Brian Binnie did it again, winning the Ansari X-Prize and raising the hopes of all that private access to space had finally arrived. But how did they do it?

There is no question that Burt Rutan is a natural genius at aircraft design. His true innovation on SpaceShipOne was the shuttlecock styled effortless reentry system, and in particular, the ease of replacing these two large booms after a few flights to mitigate wear. SpaceShipOne/Two is a glider, and just like the Space Shuttle the wings are "only" used on the way down. There are wings used on the way up, of course, they are on WhiteKnightOne/Two, but once separated from the carrier aircraft the only lift is generated from the rocket.

As smart as Burt Rutan is, he's not a rocket guy. For SpaceShipOne he tur…