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Just a minor correction, RobertDyck: That figure of 2.78 m/s^2 for Mercury's surface gravity is inaccurate. In fact it is 3.70 m/s^2, almost identical to Mars. You can confirm this by plugging the mass and radius of Mercury into Newton's law of gravitation, or check this list of Mercurial facts & figures from NASA. Due to the way the math works out, Mercury still has a significantly smaller escape velocity than Mars (4.25 km/s vs 5.03 km/s), so your argument still has merit.
I just got word that MAVEN has obtained an exemption for immediate and full reactivation to support launch at the beginning of our window on November 18th. Looks like we're back in business!
And though it is a bit moot now, you're welcome to quote me, Josh; I don't think there's anything in my post that the higher-ups haven't mentioned or alluded to in the press already. Well, maybe not the justifications for getting an exemption, but those aren't exactly a secret.
Thanks for your support guys!
We are definitely concerned here. We do have some schedule slack, and people are willing to work double shifts and weekends to get things back on track, but we can only absorb so much delay. If this drags out much more than a week we'll start freaking out. If things get really bad we might be able to swing a some tricks to extend our launch window a few days: the payload is actually slightly less than what the deltaV numbers were originally run for so there some slack there, and we could also do a less-than-desirable orbital insertion at Mars, but those would be last ditch efforts.
Besides the budgetary problem (we'd have to pay people to be on the mission for 2 extra years), there's good science reasons why delaying 2 years would be terrible. We'd be getting to Mars at dead solar minimum, when the atmospheric escape processes we're studying would be inactive and we wouldn't see much variation over our nominal 1 year mission. Our saving grace politically could be that our ability to act as a relay for ground missions is being depended upon for the future of the Mars Exploration Program (a much bigger deal than MAVEN alone), and delaying 2 years would throw a wrench in those plans.
We've got people working the politicians hard to get an exemption by the end of the week to continue work, but it's not for sure yet. Stay tuned.
Midoshi:
Did you survive the floods OK? Been worried about you!
GW
Yes, I'm fine thanks. The apartment building I live in is not far from the Boulder Creek, but the land here was high enough that we did not need to evacuate. At no point did we loose power, but the main sewer line did get clogged temporarily. It was pretty intense; the creek was carrying over 5,000 cubic feet per second, which is ~100 times its normal flow for this time of year and well over 2 times the previous record in 2003. If I step outside, even now there is a load roar coming from the creek a few hundred feet north of here; normally you can't hear anything.
It's somewhat ironic, seeing as we've been in a drought recently. Since folks on the forum here are scientifically minded, you might enjoy checking out this graph of the Boulder Creek discharge rate over the past month, along with the 26 year median (just scroll down a bit):
http://nwis.waterdata.usgs.gov/co/nwis/ … o=06730200
And yes, that is a log scale.
GW, I was the fellow you sat across from when we had dinner at the pizza place Friday night. I met Josh first, and nobody used my internet handle in person, so I'm not surprised you didn't get the connection.
I did manage to come around Saturday for the afternoon, but didn't bump into anyone I knew. After the end of the plenary I went to the session that started with the talk on the cubesat mission. Sadly, I wasn't able to make the banquet due to preparing for a MAVEN instrument science team meeting.
Actually, we just finished the team meeting here in Boston an hour ago. Things are shaping up well; looking forward to launch!
I was reminded at the meeting that I can invite friends to the MAVEN launch (window begins November 18th). Would anyone care for an exclusive NASA invitation to the MAVEN launch at Cape Canaveral? If so, just PM me with your full name and a valid e-mail. Be sure to contact me by the end of the month so I can get it submitted in time.
OK. I'll be wearing glasses and a grey "College of William and Mary" T-Shirt with a small MAVEN button near my collar.
That works too, I know where that is. So, meet there a little after 5pm?
I'd be up for that. There are a lot of options downtown, though it will be pretty hoppin' on a Friday night. Probably best to meet somewhere and then scout out a venue for dinner. Maybe rendezvous at the information kiosk where 13th and Pearl intersect? Figure out a time that works tomorrow and I can head there after work.
I'm really busy this week, so I only purchased a one day pass, which I plan to use Saturday. But I'd be happy to meet up with anyone on Friday afternoon/evening as well.
So, Ixxx?
Haha, yes, I suppose so.
I test pretty oddly on these. I am solidly Introverted, but everything else is on the fence. The tests that break down your S vs N, T vs F, and J vs P scores always have me almost perfectly balanced. That said, my tendencies tip me toward INTP.
Robert Zubrin has maintained the radiation problem has been overblown. Does this MSL evidence support that view?
Bob Clark
The main problem with radiation is the uncertainty in what constitutes an acceptable dosage, with a subsidiary question of how to provide shielding adequate to achieve that while maintaining all other engineering constraints (mass economy, structural strength, etc.). Given this uncertainty, many people either underestimate or overestimate it, brushing it aside or claiming it is a showstopper. The impression I got from Don's presentation and the following Q&A session was that we can probably deal with the radiation. However, we are still at the stage where we need to better characterize it and it's effect on humans before we actually start designing a flight-worthy system for dealing with it during interplanetary cruise.
No, I'm now at LASP in Boulder, CO working on the IUVS instrument for MAVEN. But let me know the next time you're in town and I'd be up for grabbing a coffee. And I can let you know when I next have a reason to be near the Valley.
GW:
Kepler is in an heliocentric orbit trailing the Earth. It has a period of 372.5 days, and was specifically put in that orbit to avoid interference (both gravitational and electromagnetic) from Earth and the Moon. While it will come "back around" on its own in about 50 years, that's a bit long for the current situation! Since it's in an Earth-like orbit there is a nearly linear trade-off between delta-V and mission time.
The reaction wheels are mounted in an external and accessible location. However, I can't speak to how difficult it would be to deintegrate and install a new one.
Kepler is actually operated from where I work - the Laboratory for Atmospheric and Space Physics. We got an internal e-mail about the situation the day it happened, but I think all the info it contained has since been disseminated in the press. I haven't stopped by the mission control room recently, but I bet it's pretty hopping right now.
You are welcome! I am glad someone else found it useful.
I too was disappointed by the 20 km/s delta-V limitation. On the other hand, I am very impressed by the gravity assisted trajectories it has cataloged. This makes it particularly useful for playing with Outer System missions, where a slingshot maneuver or two is standard fare, but rather challenging to compute for the typical space enthusiast.
Thanks for that summary of the info gathered. V. interesting. Confirms my general impression. Would you agree there is really more of a problem on the Mars surface, in terms of explorers being exposed on a daily basis. But that too can be taken care of through shielding of habitats and vehicles.
I think the real health threat is much more the effects of gravity. It's a bit of a roll of the dice to assume that being in third gravity will protect the first settlers.
It depends on how long the mission is. The mission design for a "long" trip would have about 200 days of cruise to and from Mars, and 600 days on the surface in between (so ~1000 days total). All else equal between spacecraft and surface habitat conditions, the explorers are exposed to less radiation while on Mars, and wind up accumulating about as much radiation damage in cruise as during their time on Mars. On the other hand, if you're doing a longer tour on Mars (in the extreme case, a one-way trip), then the radiation received while on the planet will easily dominate the total dose. As you point out, a significant amount of that could be attenuated by intelligent shielding of living and working areas
Yesterday I attended a seminar given by Don Hassler, the PI for the RAD instrument on MSL. The topic was the radiation flux observed during cruise from Earth to Mars, and what conditions have been like on the Martian surface.
The fairly constant background of Galactic Cosmic Radiation (GCR) dominated the cruise dose, though he pointed out that if you had a big enough solar flare it could have delivered a comparable dose (they did in fact see 5 moderate flares during cruise, but they contributed only ~5% of the total amount of radiation).
Being inside the MSL capsule in cruise provided a significant amount of shielding, comparable to that on the ISS (something on the order of 20g/cm2). About 500 mSv was accumulated during cruise, which would be roughly half an astronaut's typical career allowance. Don mentioned that a manned cruise would be designed to be shorter for than a robotic mission, and pointed out that shielding around sleeping quarters using drinking water/propellant tanks could significantly reduce the amount of radiation received.
On the Martian surface RAD has seen radiation fluxes values ~1/2 of what it did in cruise. This is basically because half the sky is blocked by the planet. The thin Martian atmosphere itself offers a level of protection comparable to the MSL capsule structure.
I am actually now working and living in Boulder, CO. So I will be looking into attending this August. It really is a nice town. I look forward to meeting any NewMars forum members who are able to come!
How much light reaches a terrestrial planet's surface depends on what the atmosphere is made of and how high the pressure is. Rayleigh scattering starts to reflect substantial amounts of light away from Mars once you give it a CO2 atmosphere thicker than ~0.1 bar. This is because CO2 scatters light more effectively than N2 or O2 (it is a larger molecule), and Mars' low gravity means that 0.1 bar translates into a pretty large column of atmosphere (almost 3 times larger than it would be on Earth). By the time you reach a 1 bar CO2 atmosphere, Mars (without clouds) would reflect a greater fraction of incoming light than modern Earth does (with clouds). This is actually a major problem for climate modeling scientists (like me) because the cooling effect from increased reflection overcomes the additional greenhouse effect of CO2 and makes it difficult to explain how Mars was ever warm enough for liquid water in the past.
An N2/O2 dominated atmosphere would have less of a problem with Rayleigh scattering, but you would still want to keep your total surface pressure lower than that of Earth. Of course, as RobertDyck mentioned, clouds are also a very important determinant of how much light gets to a planet's surface. Unfortunately, they are also the least well understood aspect of climate modeling, and predicting what the cloud cover of a terraformed Mars will be is a very uncertain business.
NASA just released an online 'trajectory browser' which generates spacecraft trajectories from Earth to the planets and known small bodies in the solar system. It does have some constraints, such as being limited to missions launching before 2040. However, I think it is a powerful and useful tool, especially for those without the time for experience needed to do the calculations themselves.
You can check it out here:
http://trajbrowser.arc.nasa.gov/traj_browser.php
Hi GW
Yeah, I haven't been around much lately. Lots of major life changes recently (mostly for the better).
Sounds like you've made some interesting progress on the heat shield issue. How difficult is it to process the aluminosilicate material from ore? Do you think is this something that could realistically be manufactured on Mars within a couple decades of having a permanent presence? If not, it wouldn't be a show stopper, since worn out shields could just be replaced back on Earth at the end of their lifespan.
This mission reminds me a bit of the manned Venus fly-by that was proposed in the mid-60s, which was based on using the available Apollo hardware. That mission would have been somewhat shorter at 400 days, but still pretty comparable in length and scope. It's not as glamorous as landing, but it's a crucial step in that direction. It will get the human element involved in planetary exploration, which is important in capturing the public's imagination. Don't get me wrong, I love our robotic rovers and satellites (working on MAVEN is paying my bills for the next few years)...but it will be absolutely thrilling when we get back footage of an astronaut peering out of a porthole and seeing world that isn't Earth.
Terraformer,
Yes, we did manage to regain some of the Minimal Martian Terraformed Atmosphere thread. I addressed some of the issues regarding nitrogen in this post. The review of mammalian response to elevated CO2 levels that you referred to is a few posts before that.
By the way: Sorry I haven't been posting recently! I just got a new job as a research scientist on the MAVEN mission, and we're pretty busy making sure we're ready for launch next year.
The problem with CFC is when the decomose they release free chlorine (Cl). That breaks down a lot of ozone before it gets removed from the upper atmosphere. That's why CFCs were banned, not global warming.
Yes, and the paper ultimately rejects all the Cl containing species because of the O3 destruction problem. Their recommended mix of greenhouse gases consists of CF4, C2F6, C3F8, and SF6.
Koeng wrote:I agree with you louis. The public votes on the people who decide their funding.
The only problem I can see is the data transfer rate. But then again, I don't know.
-Koeng
Just a thought - is the data transfer rate limited by failure to work with ESA who still have a satellite going around Mars? If NASA and ESA worked together could they really raise their game?
Mars Express is in a highly elliptical orbit which is terrible for regular data relay, and NASA primarily considers it as a contingency option.
The upcoming Trace gas Orbiter (TGO) was intended to act as a Martian communications relay, and was an intimate collaboration between NASA and ESA. I was actually involved in payload selection, very early in the mission design, which was exciting. We had a bunch of Europeans and Americans physically in the same room talking and working together; it was great. Unfortunately, NASA has now been forced to bow out of the arrangement due to budgetary restrictions.