About Those Decadal Surveys …
#math #physics #astronomy This looks very interesting. I do wonder if Pluto was still considered to be a planet when they started, and if it would have had a much harder time getting funded if it was only a "dwarf". https://t.co/270AZ46Aq0
— New Leibniz (@NewLeibniz) April 5, 2018
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Keith’s note: I agree with Alan Stern. I doubt that the mission would have ever been sold were it not for “the last planet we have not visited” meme. Visiting something described as being somehow less than a planet (or less important/interesting than a “planet”) – for nearly a billion dollars – would have been quite a stretch – and it was a big stretch to begin with.
Love Dr. Porco’s contributions to planetary science, but she is wrong on this. The Decadal was certainly not the driving force behind getting New Horizons to the pad–that was Stern and Senator Mikulski’s earmarks. Stern’s exactly right–if Pluto was not the ninth planet there’s no way the earmarks and political support would have kept it alive.
Many, many people and orgs helped make the exploration of Pluto possible, it was much more than myself and Sen. Mikulski. In fact, NASAWatch played a key role itself.
I agree. I doubt that the mission would have ever been sold were it not for “the last planet we have not visited” meme. Visiting something described as being somehow less than a planet (or less important than a “planet”) – for nearly a billion dollars – would have been quite a stretch – and it was a big stretch to begin with.
OTOH, the then mere asteroids Ceres and Vesta were seen as important enough to earn their own mission. And the mere moon Europa is seen as being so significant it has its own Senator.
Assuming this Disqus account is actually Alan Stern, I’d like to ask a question:
Why do you lie to the public about the IAU definition of planet? Especially the “clearing the neighbourhood” part. For example, you keep making public comments like (paraphrasing) “Jupiter hasn’t ‘cleared its neighbourhood’ because of the Trojan asteroids”. And yet you know that the language they used, indeed, the entire definition (except the names) came from your own paper with Harold Levison. You created the language “clear its neighbouring region” to define the difference between the 8 planets and the lesser bodies. Why lie to people and pretend the phrase means something that you know it doesn’t?
[For anyone else, the paper I’m referring to is: Regarding the Criteria for Planethood And Proposed Planetary Classification Schemes. — Stern, Levison, Transactions of IAU 2000. Especially the section “Towards Higher Resolution: A Proposed Dynamical Classification Scheme”.]
The only difference between the scheme in yours and Levison’s paper and the IAU definition is that you used the terms “Uberplanet” for the 8 planets and “Unterplanet” for the dwarf planets. That’s it. The names are different. Everything else is yours. So why lie about it? Even if you’ve changed your mind, why mislead people on the nature of that large gap between dynamically dominant objects and non-dominant ones. Surely it’s an opportunity to increase the public’s understanding of this really interesting consequence of planetary formation, rather than trying to actively harm people’s understanding.
You clearly felt “the gap” was important enough to write a paper about it, important enough to separate objects into dominant and non-dominant, so why actively lie to the general public about that?
I’ll add another question:
Why do you keep implying that the two “sides” of this supposed debate are astronomers vs planetary scientists, and that you speak for the planetary scientists?
You know that the vast majority of planetary scientists disagree with you. Example, Carolyn Porco, above, is a planetary scientist. (I’ve yet to encounter a working planetary scientist who agrees with you. Indeed, most I’ve been able to speak to seem to personally dislike you because of your behaviour on the issue. You seem to have trashed your reputation within your own field, with your own colleagues. All over a name.)
Then let’s declare Eris as Planet 10 already so we can get a mission to that unseen world!
I wish the flyby of Pluto was marketed more as the beginning of our exploration of new worlds in the Kuiper Belt, rather than as the closing chapter in our initial reconnaissance of the Solar System (as I recall Bolden characterizing it on the night of the flyby). The awesome photos from the flyby made me more eager than ever to see the other big worlds out there, e.g. Makemake and Haumea, but I can’t recall ever seeing the discussion of the flyby pivot towards that end.
Fly-by missions to Eris, Makemake, Haumea, etc. beyond Pluto is doable with basically with an instrument suite similar to the one on the New Horizon on a common spacecraft design. The Delta-V required for such missions just got a lot cheaper and even more cheaper in the future.
However the Deep Space Communications Network is not adequately resourced for more than one beyond the Icy Giant mission at a time.
There is inadequate Plutonium stockpile for making enough RTG for more than one beyond Pluto mission at a time. Maybe the Kilopower mini fission reactor could replace the current MMRTG RTG need for Plutonium with enriched Uranium instead.
The biggest issue with any beyond Pluto mission is getting funding for a mission lasting more than a decade. In case of the US, several Presidential terms and many Congressional turnovers.
Oh, Dr, Porco is wrong that New Horizon getting a mission if Pluto wasn’t a planet. At least not without more descoping.
The Deep Space Network could support three New Horizons-like missions at a time, as long as they were targeting very different parts of the Kuiper Belt. There are three complexes and they don’t see the same part of the sky at the same time. Of course, that would be a serious constraint on every other (non-Kuiper Belt) planetary mission.
Similarly, we’ve got enough plutonium for more than one New Horizons-like mission at a time. NH used one MMRTG and the upcoming call for Discovery proposals will allow the use of one or two MMRTGs. And that’s holding enough units in reserve to cover possible future missions until the new production really kicks in. But, again, using up the available RTGs on multiple Kuiper Belt missions would serious limit what other missions could do.
Beyond Pluto missions will not get priority on the DSN over all other planetary mission IMO. What you need is new dedicated communication assets off Earth.
The New Horizon used a leftover GPHS-RTG spare from the Cassini mission with slightly reduced Pu content that produce about 200W at Pluto.
The MMRTG (100 We output) and even the ASRG (140 We output) are not really suitable for beyond Pluto missions upon reflection. They just don’t produce enough electrical power to sustain high bandwidth data transmission that modern storage device can hold.
Some NASA mission design for a Kuiper Belt object orbiter calls for 4 MWe of power (about 36 MMRTG equivalent)
The NH spacecraft got a puny 8 gigabytes of data storage as compare to current multi terabyte SSDs. The NH data transmission rate of 1 kbps is mind numbing slow. What ever future spacecraft goes beyond Pluto should have data transmission rates in the 10s of Mbit/s range at a minimum. The NH Pluto flyby data set of 6.25 gigabytes took over a year to uplinked.
Seems a 2 or 3 kWe Kilopower fission reactor with enriched Uranium is better choice for outer Solar system spacecrafts if they come online. Mainly to power up the radio transmitters with high data rates.
The question was about flying New Horizons-like missions. Now you’re saying that’s not good enough and the next Kuiper Belt mission should be vastly more capable. I don’t think that’s a good idea. Like asteroids, there are lots and lots of them, and they are probably all different. I think that calls for adequate data from many spacecraft going to many targets, not incredibly fantastic data from one spacecraft going to one target.
In any case, 8 gigabytes and 1 kbps isn’t so terrible. Cassini had 0.5 gigabites and about 30 kbps to a 34-m station. The first project I worked on, Galileo, was stuck with 40 bps (yes, bits per second) to a 70-m station. In some cases, such as Kuiper Belt objects, there are limits on how much data you can collect. The distance from the Sun and the size of the telescopes (limited by available mass) pretty much require long exposure/integration times. And missions like New Horizons would be fast flybys. That means there is a real limit on how many images they can take.
Power is an issue, and it does impact downlink rates. But I’m a fan of using software and computer power to solve that. Data compression and on-spacecraft processing aren’t very sophisticated at the moment. At least not by the standards of today’s internet. There is plenty of room for improvement, and I think that’s a better solution then pumping more RF watts out the antenna.
For other uses of power, the past two decades have seen a tremendous improvements in low power electronics. Not all of that has passed on to flight-rated hardware. But compared to what they could build in 2001-2006 (when New Horizons was built), I’m fairly sure we could do the same thing for less power.
fcray say: The question was about flying New Horizons-like missions. Now you’re saying that’s not good enough and the next Kuiper Belt mission should be vastly more capable.
Not much more capable. Just a power system that generated more electricity without the decline in output due to aging RTG thermocouples over time along with the hassle of Pu238.
fcray say: In any case, 8 gigabytes and 1 kbps isn’t so terrible.
Take the next place the New Horizon will visit, 2014 MU69 (aka Ultima Thule). It will take about 18 months to upload the data set according to the NASA website timeline. So will any other future spacecraft in the Kuplier belt with radio transmitter similar to the 12 watts ones on the New Horizon, if not longer. There is a risk the spacecraft could go down during the upload period or the data being degraded by cosmic backround radiation. Never mind the total download time needed groundside.
fcray say: Power is an issue, and it does impact downlink rates. But I’m a fan of using software and computer power to solve that.
Will be better with the raw data. Data compression usually cause some loss of data. Having a more powerful communication system means less time required to upload the data set which will definitely be greater in magnitude than the 6.25 GB data set from the New Horizon. (note – think you meant uplink rate, since downlink rate is receiving data rate)
“Not much more capable. Just a power system that generated more electricity without the decline in output due to aging RTG thermocouples…”
You were the one who brought up multi-kilowatt and even multi-megawatt power systems. That’s a factor of ten to ten thousand more capable. Not just a little bit more.
If you’re really worried about a spacecraft dying before it can downlink the data (and that from a spacecraft which has been in flight without problems for a decade), and really think six versus eighteen months is critical, then we’re talking about a factor of three (not ten to ten thousand.)
The whole things a bit moot. First, the DSN is pushing everyone to shift from X to Ka band, and saying that (all things being equal) the data rates will go up by a factor of four. I question what they mean by “all things being equal”, but it’s probably enough to soak up that factor of three you mentioned. Second, you then go on to talk about a “data set which will definitely be greater in magnitude than the 6.25 GB data set from the New Horizon.” So much for not asking for a vast improvement over New Horizons, as opposed to New Horizons-like and looking a different KBO.
Also, data compression does not inherently mean loss of data. There are many sorts of completely lossless data compression, some used on spacecraft today and some which do a much better job of compression, but which have never been used on spacecraft due to limited CPU power. And there are clever things to do with lossy compression to reduce downlink.
(Sometimes, it isn’t clear which images are worth sending down. When the scientists who designed the observation weren’t sure about the integration time, they sometimes bracket. That is, take several images with different integration times, to make sure one is usable. Send down lossy compressed thumbnails, select the good one, and then send that one down with lossless compression.)
Finally, in all the time I’ve been at this, I don’t think I’ve never heard someone in the field talk about uplink and downlink from the spacecraft’s perspective. If the data is going up from the Earth, it’s “uplink”; if it’s coming down to the Earth, it’s “downlink.” Things can get confusing enough without having to ask “do you mean downlink from our point of view or the spacecraft’s?”
“Data compression and on-spacecraft processing aren’t very sophisticated at the moment. ” – one scientist’s noise is another scientist’s data, and when you compress, you’re making a decision about whose bits are more valuable.
The dominant power consumption for the downlink is the RF amplifier. TWTAs are a mature technology available for any frequency and power and a good working number is 50% efficiency. Sure, the electronics that makes the signal and does the modulation has gotten more efficient, but that’s going from 10 watts to a few watts. A 50 W amplifier with 100W DC power draw dominates the discussion.
NH uses a 12 W TWTA into a 2.1m dish for the downlink to get its 1kbps downlink (the requirement was 600 bps).
If you want 10 Mbps, you’re going to need 10,000 times the EIRP. I think a 120kW transmitter is out of the question.
Maybe you go to Ka-band and pick up an instant 12dB from increased antenna gain (at the expense of needing better pointing). Maybe you use a slightly bigger antenna. Maybe you bump your electrical power and get 100W out of the TWTA (requiring about 250 W DC bus power), there’s another 9 dB. So now you’re up to around 100 kbps. And that’s about where you’ll be, barring sending some Prometheus like behemoth.
The pressure on the DSN is enormous, though. There are many, many missions using it, and contention for DSN time was a significant issue for the last mission I was on. As the mission aged, our priority in the queue slowly fell, particularly against other missions with time-critical events. We started having to plan around when DSN time was available, and not vice-versa. We really need to start putting optical relay points at some of the obvious locations: Mars, Jupiter, L2. I have also been on several science mission proposals that basically were infeasible due to limitations in science downlink bandwidth.
I know. One of the things I’ve been doing for the past couple decades was planning observations for Cassini. DSN time is a huge issue. I wouldn’t want them to support multiple New Horizons-like missions at the same time; it would impact every other planetary mission too heavily. But it would be technically possible.
As for relays, I’m not sure I like optical communications. Specifically, we don’t have the telescopes on the ground to support multiple missions. At radio frequencies, we’ve got eight 34-m and three 70-m antennas operating, and two or three more under construction or planned. I think there is one telescope currently set up for optical communications. So I’d rather make those relay satellites at Mars and other places use Ka band radio.
The way to do the optical relays is to place the actual telescopes for the optical leg in space, then use radio to relay from them to the ground. That way you don’t have to deal with weather, etc, causing telecom outages. There was a proposal from JPL to do exactly this with those paired NRO telescopes.
Using the NRO telescopes wouldn’t have been free, since the detectors for optical communications aren’t trivial. But regardless of that, it only gives you two receivers and they’re not currently in place or funded for development. Until they are, a relay in orbit around Mars will need to use radio.
“Support”, though, would be vastly different during the cruise phase than during the pre- and post-encounter phase. Surely, as long as you staggered out the individual encounters, it would be no harder supporting a dozen New Horizons-class KBO missions than supporting a single orbiter like Cassini, say.
Not if the requests are like the New Horizons Pluto encounter. It’s been a while, but they wanted constant 70-m coverage for (if memory serves) a couple months centered on the encounter. There’s some justification for that, since that was their entire mission. In contrast, as an orbiter, Cassini had more flexibility. Even in prime mission, the normal practice was one, eight hour track per day, and only one in four (on average) were 70-m stations.
Nor was the New Horizons request a huge surprise. That, and things like Mars missions entry, decent and landing phase, are things people know about well in advance. We know those missions are going to want lots of antenna time around then, and they’re going to have a priority. Internally, most of the Cassini planning groups intentionally shifted observations around. We moved things that require high data volume out of the more conflicted times (especially times like the Pluto encounter or a Mars mission EDL.) But even if you stagger that series of KBO missions, there wouldn’t be any less conflicted times to move observations into.
If we want more exploration of the Kuiper region, and beyond, perhaps it is time to look at alternate, non-chemical propulsion technologies.
For instance: has anyone been following PROSCIMA, the attempt to create a mirowave beam reliably collimated at distances reaching hundreds of AU? Forward and Benford have been working on microwave propulation for many decades; it is a natural progression. And, it is essential if Breakthrough is to succeed.
This kind of tool, with appropriate spacecraft, offers a new approach. Much of the thinking is a by-product of Breakthrough, which has eschewed the kilogram-level platforms of Cassini et.al. (simply as a consequence of inadequate energy levels) in favor of much smaller craft. Much remains to be done, of course, but the theoretical background is being established.
Here’s a good place to start (in fact, centauri-dreams.com is THE web site to watch for accessible reporting on these new technologies):
https://www.centauri-dreams…
Chemical rockets finally begin to reach a truly useful scale (FH, and of course BFR). It’s natural to look beyond Pluto. And this is exactly the type of project that Dr. M. so often favors.
A great time to be alive.
In theory if someone have the cash and there is Mars ISRU propellant production. Expendable deep space rockets based on the 2016 SpaceX ITS specifications could be staged from Mars orbit.
Something like three half size ITS booster cores with single engine of about 3500 tonnes gross mass each. Arrange like tri-core heavy rocket. The outboard cores ignites and burn out then get discarded before the center core ignites. The payload could be an outer system object orbiter of about 4 tonnes and a low power electric propulsion module. The propulsion module is in effect a departure stage from Mars and a retro stage on arrive at destination
This is a big rocket achieving high velocity with lots of impulse with a small payload starting from a weak gravity well (Mars) further out in the Solar system.
All you need for this to be variable is come up with 10 kilotons of propellants and delivered it to the Mars orbital launch location.
I understand that even bigger rockets, like what you describe, are likely to appear. Still the era of rockets is coming to some sort of logical zenith, mostly because our interests are taking us further than the biggest rockets. Nobody contests the need for alternative propulsion.
Breakthrough is so cutting edge it’s breathtaking. Can’t wait to see what this initial round or research learns.
Alternative propulsion for manned missions is not that many and have techno or political huddles to clear. So some sort of big spaceships with high propellant mass fraction will be around for a while along with many propellant depots. At least until there is a working space nuclear reactor with multi mega watts of electrical output.
Have doubts about the whole Breakthrough concept. Not getting the probes to their destination. But how much useful data can be gather by sensors that will fitted onto the probes and getting those data back. Then there is the expected high attrition rate of the probes during the mission.
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What is laughable is how the man who dreamed and then DDT&E the mission to Pluto doesn’t have a validated twitter account.
Stern is the real deal. And he has class.