Hi all, I thought I'd start a thread for people to dump questions that they might think are good for Planetary Radio. Planetary Radio is The Planetary Society's weekly half-hour podcast. It features an interview by producer Mat Kaplan with a space scientist, engineer, advocate, or well-wisher, and three regular segments: news headlines, "What's up" with Bruce Betts, and a Questions and Answers segment that I read. Each week, Q and A addresses one question, with half of the answer given at the beginning of the show, and half toward the end, each half lasting between 1 and 2 minutes. I get lots of questions submitted but the majority of them can't easily be answered in this rather strict format, so I am always looking for more questions.

So, please post your questions! They don't have to be questions that you don't actually know the answers to -- also please consider submitting questions your friends and family ask you, as those are often some of the best. And, if you see a question here that you can answer, please don't hesitate to answer it and save me a little research work!

--Emily

How do they do TCM's with spacecraft that are spin stabilized like MER?

That could be the part two, to a more general look after spacecraft on their way to Mars -does Phoenix have only one fuel supply which is used for cruise and landing?

Both questions for which I have NO idea to the answer!

Doug

Typically via pulsed thruster firings timed to the spacecraft's rotation, which allow the spin axis to precess to the desired attitude. If a velocity change is desired as well, then a coupled thruster firing is performed once the spin axis is set.

Hey, maybe we should start a separate thread to come up with some harder space trivia questions for Mat and Bruce.

In fact, why don't we turn it around, i.e., we ask the questions and see if the two of them can answer them. If they can't, the originator of the question gets a free TPS T-shirt

That'd be cool!

Here's one I always wondered about: how exactly do Cassini's hemispheric resonating gyros (HRGs) used in the inertial navigation system work?

A-10s use something called a vyro for their stability augmentation system, which is basically a strip of a niobium alloy that's vibrated @ a high freq by piezoelectric drivers. Very similar transducers then measure the amount of force generated 90 deg from the drive plane to determine rate of motion. I suspect that the HRGs work much the same way, but from the name the geometry sounds a little weird...

In principle, here's an excerpt from this paper:

QUOTE

One of the most well known examples of the oscillatory gyroscope with continuous vibrating media is a hemispherical resonating gyroscope (HRG). HRG sensitive element design usually is based on the resonating shell that has a hemispheric or so-called “wine-glass” shape. Primary oscillations are provided by standing wave excited in the rim of the shell. In case of no external angular rate, nodes of the wave do not move. If the sensitive element rotates around sensitive axis, which is orthogonal to the plane of the wave, the secondary oscillations can be detected at the nodes. Despite HRG itself has never been referred to as a micromechanical gyroscope, its operation principle has been widely used in the number of micromechanical designs. In particular, the hemispherical shape of the shell has been replaced with a thin cylinder or a ring.

Note also an excerpt from a Northrup Grumman press release:

QUOTE

The hemispherical resonating gyro utilizes a thin-walled quartz shell that is energized by an electrical field to produce an imperceptible vibration pattern within itself. This pattern is electrically sensed and used to determine the gyro's output parameters. The vibration is so minute that it creates virtually no internal stress and fatigue effects, leading to its unmatched reliability. Northrop Grumman is the exclusive producer of the gyros, which to date have accumulated more than 4.5 million hours of operation in more than 50 systems in space without a mission failure.

Or check out the Northrup Grumman HRG web page.

Answered by our ever-knowledgeable Reference Librarian! Thanks, Alex. Pretty cool technology; maybe it's Planetary Radio-worthy if explained with analogies.

Here's a quickie: Why does Mars have such huge volcanoes? Ans: No plate tectonics, with maybe a discussion of the Hawaiian volcanic chain by way of comparison.

Wait a minute...why the hell doesn't Io have huge stratovolcanoes? Ans (?): low crustal tensile strength (and/or the crust is very thin indeed), different materials?...

I heard that Phoenix in going to land inside Mars' Arctic Circle.

Does it mean it will certainly stop working as soon as the "very long night" comes, and when exactly it's going to happen?

This is a question that I hear (in various forms) a lot, so I think it's an excellent one for Planetary Radio. I've got some answers on the mission facts page and in the last paragraph of this article.

I like the TCM question but will need a little help on answering that one; thanks for the beginning, Alex.

Big volcanoes is a good one too...

The HRGs one is probably a bit too technical for the format.

And Alex, I like your idea; send it to Mat and see what he says! It'll get a chuckle, if nothing else.

--Emily

A combination of lava with low viscosity and a short life-span for individual volcanoes compared to those on Mars.

Just out of curiosity, what do you mean by format? Is there a base level for "difficult" questions beyond which you don't wish to go (i.e., least common denominator theory for audiences)? Or is it simply due to the time constraints for your Q&A segment? Or both? Or more? Etc.

When can we expect to observe features on Eris with clarity comparable to HST's images of Pluto or Ceres? Is it more likely to get such views from a telescope or a space probe?


Paolo Amoroso

After posting the HRG question, I realized that PR is a mass broadcast intended for a general audience. Don't think it's a question of dumbing down, but more about engaging an intelligent, interested audience who probably aren't all that familiar with the wonders of the Solar System and UMSF to anywhere near the degree that we regulars are (if I may place myself in your distinguished company!)

Emily, thanks for setting this thread up!

I've had a question about Cassini-Huygens, and the release of the Huygens probe. Why did it release the Huygens probe so early in the mission?

After launch, the riskiest moment of the voyage occurred when C-H first arrived at Saturn, when it flew through the ring plane. Once it got into orbit, the danger of a catastrophic accident diminished greatly.

The release was delayed an extra orbit to allow Cassini to get into a better trajectory for receiving the Huygens signal, but no one knew if the probe would land in a sea of methane or on solid ground. The probe was still transmitting when Cassini flew out of signal range, prompting me to wonder why they didn't wait much longer, until the primary mission was further along or even mostly over, to release the probe when they could put Cassini in an even better trajectory.

A few months after the probe was released, Cassini made a much closer flyby of Titan. Wouldn't it have helped to fly past Titan several times to scout for some potential locations before releasing the probe?


Attempting to answer:
One of my buddies at space.com suggested that hanging on to Huygens even for one extra orbit burned up a significant amount of reserve fuel, and there was a lot of other exploring for Cassini to do around the Saturn system. I read a status report from soon after the probe was deployed that supports this point.

I appreciate if anyone can run this question by someone on the Cassini-Huygens team!

By "format" I mean what I described at the top of the topic. The show is intended for the "interested public" but it is broadcast on Public Radio stations, so whenever I use a word that might be unfamiliar to the general public, I have to take the time to define it (or euphemise around it). With the HRG question, I'd likely spend all the time defining, and wouldn't have enough time to actually answer the question.

--Emily

I believe you are referring to this thread, right? FWIW, Calli's answer over there is the standard answer that I've always heard (i.e., delta-V penalty later in the tour maneuvering a heavier spacecraft, reliability, etc.).

Thanks for the answer. I was just curious, not being a radio star and all that.

That's a good one, Alex. I'd been assuming that since the Huygens landing was a fundamental mission objective that the team felt it was prudent to execute the operation as early as possible during the primary mission as a risk avoidance tactic (hearkening back, perhaps, to the Galileo probe deployment). Hindsight being 20/20, it well might have been better to do the landing after a few passes at Titan to search for interesting targets...would like to know the true rationale as well.

Can only imagine what might have been if Huygens would have landed on the shoreline of one of the polar seas...

(Just to clarify: no criticism implied at all of the strategy...the team and the mission have performed brilliantly, and it's really easy to look back after revealing the completely unknown and say "they shoulda done this, that, and the other thing"...ain't saying that at all! )

hi Alex

Indeed, that thread was my first post on space.com!

Another question: have they tried to bump the dust off the MERs? Could they run a rover up against a boulder and shake some off?

Aside from Jupiter being a much easier target to hit with an atmospheric probe than Titan (indeed, jovian gravity focusing made the hit a virtual certainty), remember also that the Galileo probe had to be released prior to Jupiter orbital insertion simply because, unlike the Cassini-Huygens configuration, the Galileo probe was mounted in front of the orbiter's main engine nozzle.

See NASA's official history of the Galileo Project here.

You mean purposely? I think I'll let someone else ask the MER team that question. And just think of all that time, effort, and money spent in developing hazard avoidance software

Okay, not slam it into something, but how 'bout getting one wheel up on a small rock, and getting it to jostle some dust off.

When I was at the JPL open house, they drove a rover over me and a bunch of kids. I stayed real still, but the kids were all wiggling, and the rover had no problem whatsoever. Those things are pretty sturdy, IMO.

I really don't know. I guess it all depends on how serious the "jostle" would have to be. Aren't the solar arrays in their deployed positions fairly sensitive to sharp forces?


Just consider yourself lucky that they didn't demonstrate drilling a RAT hole on you or test the APXS or Mössbauer on you

Ye Gods...I did not know that. Not to divert the discussion, but what a risk...

Might have been worse; if it was an MSL EDM poor Brellis could have been lasered... (All kidding aside, sounds like it was a great experience, B. )

Emily, have you considered describing (not explaining) some of the true mysteries of the Solar System? They all have hypotheses, of course, but I think that the audience might be very interested to know about them. Here's a quick list, by no means complete, and hopefully everybody can add more:

1. Why is Uranus tilted on its side?
2. Why is Venus' day longer than its year (and apparently synchronized to Earth?)
3. Why does Iapetus look like it does (might have an answer soon! )
4. All gas giants have rings; why are Saturn's so much denser than the others?
5. Why did Venus apparently lose its oceans?
6. Why is Triton geologically active? (Probably tidal heating, but in a weird, cold way...)
7. Why did Mars lose its magnetic field?
8. Why does Miranda look like it was patched together?

Regarding the dust issue on the rovers, we always compare to what we see on Earth. I guess it'll be interesting to run a comparison between dust behaviour on Earth, Moon & Mars. We all know how bad dust can be on the moon. When one look at drawings of Moon exploration, you never see dust on the astronauts. When you look at the actual pictures, you're amazed how much dust they carry.... and only soalr wind to clean them up .

Yep, I have to admit these are the types of questions that fit perfectly into the "format" of PR Q&A.

You might even add:

Is the "dark side" of the Moon really dark?
Why do technicians wear "bunny suits" when working around spacecraft?
If I can run a mile in 6 minutes on Earth, how fast could I run a mile on Mars?

Although excellent for the format, they can be hard for me to do because the "answers" can be hard to write -- many of these are the subjects of dozens of papers and dissertations. And I usually procrastinate on writing and recording these until the weekend, so I'm looking for quick answers.

Not a bad idea, though, simply to present them as mysteries, explaining what the mystery is with no attempt at answering "why"...

--Emily

You bet! The idea is outreach, and grabbing people's imaginations so that they begin to develop a genuine interest in space & then begin to explore more deeply.

A lot of us late baby-boomers were exposed to extensive public awareness of space at young ages during the 60s through the media (limited as it was then) and books, and it stuck in some of us as a life-long interest. Sadly, this didn't happen for Gen X, Gen Y, and the Millennials; not only are books rapidly becoming passe to them, but the sheer volume of readily available information has exponentially increased, so focusing their attention on this particular subject has become much more difficult.

PR is one way to do this, and a good one. Old-fashioned yet still omnipresent broadcast radio's main strength these days is that it's the only safe form of entertainment available while driving, and NPR's competition is limited to at best two dozen or so stations in the most crowded markets. (Compare this to billions of Web pages & hundreds of TV channels.)

Shameless marketing strategy? Yep. Should PR answer LCD questions? Yep. Does the end justify the means? Absolutely! TPS isn't trying to sell miracle toilet paper or exploit the substance abuse problems of various celebrities for profit, they're trying to educate and enlighten people about what are arguably the most important, dramatic, and significant activities of the last 500 years: the exploration of our Solar System, and the opening of an endless frontier for our species.

You better copyright this quickly.

That or you might summarize the most popular hypothesis prefaced with "One of many possible explanations is that..." and concluded with "However, we still really don't know why yada-yada-yada, and more research is needed"...minimal burden on you!

EDIT: Thanks for the great complement, Alex! TPS can have it if it wants; space is and should be, after all, the most public of domains...

Were Kuiper Belt Objects pushed out to their current orbits?

If so, were they sent out there by the same events that pushed Uranus and Neptune out from between Jupiter and Saturn?

As fast as 1 km...since, on Mars : 1 km ~ 1 Mile ***
and this is ONLY on Mars.

*** Ok, ok, don't start again to argue about nautical and statut, etc....

Here are two other "mysteries":

-Why don't Saturn & Uranus have Trojan asteroids?
-Why is Mercury locked into a 3:2 spin resonance with the Sun instead of the expected 1:1?

Looking back at my mystery list, it's interesting that many of them seem to involve some sort of odd orbital/dynamical situation. Is this my own perceptual bias at work, or an indication that the early evolution of the Solar System (including the inner planets) was surprisingly chaotic?

Is there some physical reality behind Titius-Bode's law?

Why are Martian meteorites so relatively common compared to Lunar ones?

Are there any meteorites from Mercury?

Another oddity: Are Phobos & Deimos in fact captured asteroids, or did they form with Mars? (IIRC, some of their orbital parameters seem unusual for captures, even though Phobos is supposed to hit Mars in 100My...)

OT, but is anyone else in LA FRYING right now??! I've been running my A/C 24/7, and it's barely keeping this tiny little apt habitable...haven't been this hot in years, wondering why the hell I ever left Alaska...

Not just LA, most of the US is over 90. It'll be 100+ in Sacramento again today. Looks like I'll stay indoors and be upgrading software and dusting ceiling fans.

http://www.weather.gov/forecasts/graphical/sectors/

Ahhhhhhh - 16 deg C,clouds, occasional showers...very British. Loving it

Doug

Boy did I pick a good time to leave LA 76 and sunny with a nice breeze, and not a wildfire to be seen.

Boy, do I envy you guys that are out of this...it's unbelievable, really. Took three showers yesterday just to cool down, already on my second now and it ain't even NOON yet!

How's the humidity Tim?

Too hot ?
My son and I spend the nigth from Saturday to Sunday on a summit at 2730 m. As shown on the picture it was ...cold (4°C in the morning).
Hey, next time, come with us !
Click to view attachment

Back on topic. We know that a supernova explosion relatively "close" to the Earth will send deadly radiations. I have no idea if were're talking of lot of radiations for a very short period of time or still a lot of radiation for a long period of time. So my question is : how long those radiation will last? More OR less than 24 hours ? ...just wanted to know if a part of the Earth could survive.

Let me take a hack at this: Yes, there are, but they are probably very rare due to the fact that much less material can make it from the vicinity of Mercury to the Earth because M. is much deeper in the Sun's "gravity well"; it's an uphill battle. Moreover, Mars meteorites are not only more plentiful but easier to identify because we have good chemical/minerological models of its surface from the VLs, Pathfinder, and the MERs; we have no equivalent baseline of data from Mercury.

Your question about the relative rarity of lunar meteorites is a goody; nothing springs to mind, you'd think that we'd be tripping over the damn things, really. Maybe it's just because there hasn't been an impact energetic enough in modern times (Giordano Bruno in 1180 AD being the most recent, apparently) to eject material at more than lunar escape velocity, compounded by the fact that any ejected material reaches Earth relatively quickly? (I know, sounds thin to me, too... )

EDIT, Actually, the GB impact's aftermath might be a very interesting research subject for astronomical historians. Was there an increase in observed meteors and/or reports of 'stones from the sky' in the months after the purported impact? Recorded information from this period is sparse (from Western archives anyhow; might be better from Arabic and Chinese sources), but boy would this be fascinating to know...

Related to the question of Mercurian meteors:

In one of the panspermia scenarios, comets carrying life's building blocks "seed" all the planets.

In another scenario, life might have arisen on Mars 3 Billion years ago, which then "seeded" earth with a life-bearing piece of ejecta as a result of a gigantic impact.

How likely would it be for a Martian meteor to make it out to the Jupiter or Saturn systems on a trajectory similar to the "Grand Tour" path of the Voyagers? Now that we know the signature of a piece of Mars, could we detect such a signature on a future lander mission?

Could bacteria on a Mars (or Earth) meteor survive a plunge into Europa or Enceladus?

Unless the supernova was exactly in the equatorial plane the high latitudes of one hemisphere would not be directly hit, at least not by X-ray/Gamma radiation. It's more complicated for charged particles. I'm not sure about secondary radiation and stuff caught in the Van Allen belts.

I don't think panspermia will work unless there is an atmosphere to brake the meteorites to a relatively soft landing. Note that it is dynamically almost impossible for a meteorite to arrive at less than escape velocity to an airless surface.

True. How about if a mars/earth meteor were on a long, lazy trip that took thousands of years, with some of those "immortal bacteria" along for the ride?

The scenario that makes the most sense is the one where comets provide the seeds of life over the course of billions of years, giving life a chance to grab a toehold if the conditions allow.

Thinking back to the now-famous Mars meteorite ALH48001 (IIRC), it burned a hole in my brain that a rock carrying a possible Mars fossil landed on earth.

Thanks for all the questions and answers, guys, and keep them coming. Those of you who are regular Planetary Radio listeners have probably already noticed that the combination of the holiday weekend, extreme heat, and my daughter's sudden decision to give up her morning nap all combined to make me unable to get to recording even a single new one this weekend. Hopefully I'll get a few of these in the bag this week so you won't be subjected to more "Classic Q and As."

--Emily