Interstellar Objects have been a source of fascination since 'Oumuamua passed through our Solar System in 2017. The study of these objects could tell us a great deal about other star systems.
Guest | Dr. Alan Stern, Associate Vice President Southwest Research Institute [@SwRI]
On LinkedIn | https://www.linkedin.com/in/alan-stern-0786409/
On Twitter | https://twitter.com/AlanStern
On Facebook | https://www.facebook.com/s.alan.stern
Host | Matthew S Williams
On ITSPmagazine 👉 https://itspmagazine.com/itspmagazine-podcast-radio-hosts/matthew-s-williams
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Episode Notes
Interstellar Objects have been a source of fascination since 'Oumuamua passed through our Solar System in 2017. The study of these objects could tell us a great deal about other star systems.
In a recent study, Dr. Alan Stern and his colleagues detailed an Interstellar Object Explorer (IOE) mission, which could rendezvous with future ISOs as they pass through our system.
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Resources
A study of an interstellar object explorer (IOE) mission (Stern, et al. 2024): https://www.sciencedirect.com/science/article/pii/S003206332400014X
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For more podcast Stories from Space with Matthew S Williams, visit: https://itspmagazine.com/stories-from-space-podcast
Rendezvousing with an Interstellar Object | A Conversation with Dr. Alan Stern | Stories From Space Podcast With Matthew S Williams
Matt: [00:00:00] The authors acknowledge that this podcast was recorded on the traditional
unceded lands of the Lekwungen peoples. Hello, and welcome back to another episode of
Stories from Space. I'm your host, Matt Williams. And joining me today is a very special guest,
noted engineer, planetary scientist, and the principal investigator of the New Horizons mission,
Dr.
Alan Stern. Dr. Stern is also a commercial astronaut, aerospace consultant, and the chief
scientist at Moon Express, a commercial space company dedicated to lunar mining and
development. He is also the author of several books, including The U. S. Space Program After
Challenger, Worlds Beyond, Pluto and Charon, and Chasing New Horizons, Inside the First Epic
Mission to Pluto. Dr. Stern, welcome aboard!
Stern: I appreciate it.
Matt: Dr. Stern, with your permission, I'd like to jump right in and discuss [00:01:00] something
very exciting of which you are part. Yourself and colleagues from the Southwest Research
Institute, you recently conducted a study on a interstellar object explorer, a spacecraft concept
that could rendezvous with interstellar objects and study them up close.
Now, first of all, can you give us a little background on why ISOs have become such a subject
of interest in recent years?
Stern: Sure, absolutely. As a research community, the planetary science and astronomy fields
have predicted for decades, literally stretching back, uh, into the earliest days of, of space
exploration, that we would eventually discover objects floating through interstellar space that
are castaways from other solar systems.
It just happened to come through our solar system and there have [00:02:00] been searches for
these in the past, which were unsuccessful, but really the technology wasn't available to do
the kind of search necessary to actually find one until 2017 when the first of these objects was
discovered.
Matt: 'Oumuamua
Stern: That's exactly the name of it passing through our solar system in 2017 at very high speed.
Another called Borisov was discovered in 2019. And although we have not found more since,
uh, based upon the two detections that have been made, we're pretty confident that with the
advent of a new observatory, it's coming online thanks to the National Science Foundation
beginning next year.
So we should detect. One to several of these per year, every year from now on, and that opens
up the possibility that we may be able to [00:03:00] get spacecraft to some of them. It'd be very
valuable to do because we've never studied something formed outside of our solar system upclose and personal with a spacecraft the way that we study asteroids and comets and Kuiper
belt objects and having the opportunity for those objects to come visit us and to get a spacecraft
to fly by them. Would be really high value science.
Matt: And this, this concept of course, it's the catching up to an interstellar object. As you said,
next year we'll be detecting more of them. And this would be because that's when the
bureaucracy Rubin observatories going to be gathering it's first light.
Stern: Yep. The large synoptic survey telescope now called Vera Rubin observatory will come
on late this year and start scanning the sky.
More or less making motion pictures of the sky down to extremely faint objects and should
catch things like this on a regular basis. Once we determine their orbits, we [00:04:00] can find
out which ones come close enough to the earth to send an interceptor there.
Matt: And in fact, the detection of ' Oumuamua and Borisov, I personally felt that just the nature
of these two objects, how they're detected rather close together in terms of just timing, that it
was really quite Indicative in a way.
It was like a ' Oumuamua confounded astronomers for quite a while, whereas Boris saw that
was clear almost right away, wasn't it? That it was a comment.
Stern: Well, we're not sure what these things are and , and having studied two of them is very
small sample. interstellar space is almost certainly teeming with ejecta from solar systems all
around the galaxy.
So there's almost without a doubt, there's a wide variety of objects out there ranging from rocks
and boulders to. Things that are the size of comets and asteroids, even up to the size of planets
that will be [00:05:00] free floating in an interstellar space. Now there are many fewer planets
than there are comet sized things, and there's still more boulder sized things.
But in the study of how solar systems form in general, Around other stars and how planets form
around other stars, we've never had an opportunity to actually see something up close to
understand its geology and surface composition and other properties the way that we have
studied the building blocks of planets in our own solar system.
And now we're just reaching the brink of having the ground based technology to find those.
Objects. And we have the space based technology, if the money's available, to build an
interceptor and go to one of them. And I think that'd be really exciting.
Matt: Absolutely, yeah. I mean, basically we would be looking at a sample from another star
system. It's [00:06:00] the next best thing to actually go in there,Stern: yeah. And it saves the long hike across interstellar space because they come close to
us.
Matt: Well, now this, this puts me in mind here. In terms of your study and the spacecraft you're
envisioning there, can you give us a quick rundown on the kind of technology it would use? Like,
for starters, propulsion.
Stern: Well, let's, let, let, let me start at the big picture and then I'll come to propulsion. First of
all, what we determined in our study is that we have the technology now that we don't need to
invent anything in order to make a mission like this possible. We just have to decide to build it
and build it.
It requires conventional power systems, conventional communications, conventional
technology. propulsion conventional scientific instruments. And the reason is, is that we're
going to go after an object coming from another star system that comes pretty close to the
earth, [00:07:00] not right up to the earth, but that is certainly closer than Jupiter's orbit.
And we're not going to try to match speeds with it. And rendezvous with it, we're just going to
make a fast flyby, like the first missions to Halley's comet back in the 80s, or like even the New
Horizons mission that I led to Pluto, where our orbit, that is the orbit of the spacecraft and the
orbit of the interstellar object, just cross on a given day, and the spacecraft gets very, very close
where it can train its cameras and spectrometers on the interstellar object.
And determine what it's made of, determine how it was formed and how it has evolved, what
its geology and geochemistry are, its density, some of its internal properties. Look for an
atmosphere around it. If it's like a comet, we'll call that a coma. Determine what that's made of
and then send all that data back to Earth for us to pour over as a first mission [00:08:00] to a first
interstellar object.
Same way that we've now made the first mission to Pluto, the first mission to a Kuiper belt
object and many missions to asteroids and comets. It was the discovery of Oumuamua and
Bortoisoft that, that really caused us to go take a hard look at how you would do this. Others
have taken a look too, and although they've come up with some somewhat different ways of
going about it, that the common thread is that it is doable, it is affordable, it is within our present
technology.
And so, uh, it's the kind of thing that NASA or ESA could choose to do and would have high
scientific impact. But I should also caution that the object we fly by may not be anything like a
corporate belt object or an asteroid or a comment. We don't know that it's just a random object
from the interstellar grab bag that we can reach and we'll have to see [00:09:00] what it's like.
That's part of the fun, but it's also, uh, just reality. We cannot tell before we get there very much
about it. And very few of them come close enough to be able to reach with present technology.
So in that sense, we're beggars and beggars can't be choosers. When we build a spacecraft
and buy a rocket and are ready to do this.We'll probably go after the very first one we can reach.
Matt: Well, in fact, that was part of your study too, was the limits of detectability and the
potential for rendezvousing with it. And as I recall from the paper, you established some
parameters and said that. That, uh, there were velocity requirements, yes, but also the likelihood
of being able to rendezvous with an object.
It got better as you're approaching two astronomical units, right, as the object itself was two
astronomical units from the Sun.
Stern: [00:10:00] Well, as the objects come closer to the sun, they're brighter and easier to
detect and track. That's the good news. The bad news is when they're closer to the sun, we
have less and less time to affect the intercept before they fly away.
So it's a fine balance between trying to search for interstellar objects far enough out to be able
to Get on the way to them before they're gone and, uh, having them come so close before their
detection that we don't have the time for that. So our solution, there are different ways to go
about this, but our preferred solution is to launch a mission into space and have it loiter, wait to
make the big final targeting burn with the upper stage of the rocket to get it on its way.
And it might wait for years while the ground based. Observatories like Vera Rubin, scan the
skies, find interstellar objects, and we cross match them against our [00:11:00] propulsive
capability until we find one that we can actually get that spacecraft to before it's gone. And
then we like the engines on that rocket and send the spacecraft already in space on its way.
And that's superior to keeping it on the ground for a number of reasons. One is getting things to
a launch pad on short order. Is a tall order. It's, it's really a real headache when launch pads
are in short supply as they are. And there are many other satellites and, and exploration
spacecraft that want to get launched.
If you just keep your spacecraft in a warehouse and it's rocket in a warehouse nearby, and
suddenly you have an opportunity to fly it to an interstellar object, your launch pad may or may
not be available. Putting it in space where you can control when you make that final engine
firing is a much more surefire way of making sure that when we find the right object to go after,
we're able to go right after it. [00:12:00]
Matt: And you sort of alluded to earlier the fact that there are other teams looking at other
proposals. And one that sort of pops for me was Project Lyra, and that was from the Institute of
Interstellar Studies and Marshall Eubanks was the principal investigator.
Now, that envisioned using laser sails and directed energy propulsion. But yeah, you guys, on
the other hand, we're looking at rockets, boosters, et cetera.Stern: Well, the team of people that, that I assembled mostly at the Southwest Research
Institute, but also some outside collaborators and Southwest Research Institute, my home
institution, have a great deal of experience in space flight.
And also a pretty high batting average at winning competitive proposals. And our ground rule
was that we should find a technique that doesn't [00:13:00] require inventing anything we don't
absolutely have to. No one has laser sails like that, or laser guns to propel those sails. And if I
wrote a proposal around that, It might get an A for ingenuity, but it would get an F for doability
and it would probably fail on, on cost as well.
So we chose to only study things that we know how to do today with conventional rockets,
conventional propulsion, conventional spacecraft, and it turns out it works. We can do it just
like we do a mission to Venus or Mars or a comet or an asteroid. And, uh, the only difference is
we're flying to a different kind of target with very special scientific importance.
Matt: In fact, yeah, that's a very key thing, isn't it? When it comes to design studies that are
actually likely to produce a mission. Can we do this today? [00:14:00] It's fair to say that's the
whole point of doing such a study, isn't it?
Stern: Well, yes. The point is that the published papers about how to do it. The point is to actually
get a spacecraft out there.
To make it fly by and discover things about the object. And as you probably know, when NASA
calls for proposals or the European space agency calls for proposals, they're very heavily
oversubscribed. They'll typically be 20 or 30, 500 to thousand page proposals detailing how to
do different missions out of which.
One gets selected. It's very steep competition. Sometimes two gets selected, but still two out
of twenty or two out of thirty is still very steep odds. And so, If you want to get selected, you not
only have to have blockbuster science, but the story has to fit with confidence within the cost
and schedule and technology base that we have.
It has to be a [00:15:00] completely airtight story that you're going to be able to execute that
mission with confidence and get the goods.
Matt: So in fact, in terms of next steps. Is there currently a plan to build on this study, hopefully
attract NASA funding, and eventually lead to a Pathfinder type mission that could actually be
ready to go in the not too distant future?
Stern: Well, in the case of NASA, the most natural program for this is called Discovery.
Discovery has been around since the 1990s, and every few years NASA asks for proposals,
which as I said, they're very detailed. They involve teams of sometimes hundreds of people,
engineers and scientists. They can be a thousand pages thick, and they typically are about that
with spacecraft design, instrument design, ground system design, trajectories, cost plans,
management plans, and much more.NASA puts [00:16:00] those to a gauntlet of green eyeshade reviews to make sure that every
aspect of it pulls water, and then they rank them. And then out of that ranking comes usually 2,
3, 4 that they will select as finalists for more study for a year or so. And then from that study of
the finalists, one, occasionally two, gets selected.
So for teams like my own that might be interested in doing this, you have to get your precursor
work done and be ready when NASA calls proposals to feel the team and write a proposal that's
going to pass through that gauntlet. And come out on top. Yes. This is ready to propose, uh, but
NASA only calls for discovery mission proposals every seven, every several, excuse me, every
several years, NASA has not announced a firm date for the next [00:17:00] time they call for
proposals and our team and others might propose for that.
But frankly, since it is very competitive, that's the kind of thing that we keep under wraps for
competitive advantage. So you just have to stay tuned. I'm sorry.
Matt: So regarding what the discovery, the detection of a Borisov set off, there were many
papers that came out from this in terms of the implications that these detections themselves
had.
And you mentioned how the number of interstellar objects that enter a system, there's
estimates on that. There's estimates on how many we could detect. There was also research
that indicated that some of these interstellar objects may actually still be in our solar system.
That over time, some that arrive get captured and they're still here.
And so that too, the prospect of finding ones that stayed, that has also [00:18:00] been proposed
as a mission idea, has it not?
Stern: I don't know anyone who's studied how to do that as a mission. It is true that occasionally
these objects are captured. Can get trapped in our solar system, but it's very rare because they
come by at such high speed it's very hard for them to get captured into orbit around one of the
planets or around the Sun and I Believe the the odds are just astronomically against that that
millions of objects have to go by in order to get Uncaptured it might be even steeper than
millions.
It might be billions or trillions, but it's extremely rare So the best way to get a mission to examine
one of these is to go after one that's just passing by, because we know that there are going to
be disparities. One to several of those every year, now that the Vera Rubin telescope is coming
online.
[00:19:00] And so that enables a way to do this sooner rather than later. If you want to find ways
to do it differently, to catch up with these objects, to orbit them, to find them orbiting a planet or
orbiting the sun, that's a much tougher problem. And it's not ready for prime time. I'm all about
pragmatism. It's better to have 80 percent of something, I always say, than 100 percent of
nothing.We want to get a mission to an object like this. We want to choose the easiest way to get a first
mission there. Then we'll worry about the second mission.
Matt: Well, actually just one other question that you put me in mind of there have been
proposals. In fact, I think this was the crux of Project Lyra. It was to catch up with Amuamua
and that there had been some speculation that done right, a mission could actually reach that
mysterious object itself and then not wait for the next one.[00:20:00]
Is that a feasible possibility at this point?
Stern: You know, I don't know the answer to that. We found it difficult. To put together a mission
that's going to fit within the budgets of the discovery program with doable technology and a
straightforward execution plan that goes after a new one that's discovered years from now,
once the spacecraft is built, catching up with one that's already long gone.
Is a much tougher assignment for one thing. By the time you get there, it's going to be very far
from the sun. Can't use solar arrays. You're going to need nuclear power like we had on new
horizons and that alone is more expensive and much more time consuming. So I don't see a
strong reason to go after a mula mula other than interest in the open problems about it when,
when we've got new objects coming through our solar system.
All the time that Vera Rubin will discover, and then we'll have the pick of the litter.
Matt: So, [00:21:00] bottom line is, our best bet is to wait for future ISOs and to have a mission
ready to rendezvous with them, than to look for those that might have stayed or try to catch up
with the ones we've already seen. I think that's right.
Yes. And well, you know, I certainly wish you the best of luck in terms of this project and others
that stand to tell us a great deal more about formation and evolution of star systems. If I could
ask you to opine there just a little bit, what we could stand to learn from an ISO, I mean, it would
be rather profound.
Stern: Well, I think we'll learn about how we'll see at least we'll see an example of how these
objects formed around some other star system. And since we're taking a random grab bag
sample, we're going to go after the first one we can reach. We have to assume that it's probably
typical of how a lot of these objects form.
And if that is like the objects in our own solar system. That's very [00:22:00] important
confirmation that all the things we're learning about how planets and the seeds of planets form
apply in many other instances across the galaxy. On the other hand, if we discover that object
was formed very differently, and its chemistry is very different, its composition that is, and its
geology, and it is very alien compared to the objects we see in our solar system, that's another
important data point.Either way, I think it's landmark. We'll just have to see what the data tells us, but I'm excited
because I think this will capture the public imagination and we know it's scientifically important
and it's actually doable. I wasn't sure when we got started if it would turn out to be doable
within the present technology and within cost constraints, but it looks like it is.
Matt: Well, that's very encouraging and I'm really happy for that result. It was exciting to read
about. So thank you for doing the study [00:23:00] and yeah, naturally I hope this will someday
lead to a mission itself.
Stern: Our, our teams was very happy with the way it turned out and. Thank you for your interest
in it. Very appreciated.
Matt: No problem. And naturally, I hope to get you back on here to discuss many, many, many
other topics of which you are well informed expert, not the least of which includes the outer
solar system, Pluto, Kuiper belt, Charon, all those wonderful places.
Stern: I appreciate it.
Matt: For those who are interested in learning more about our topic today, you can read the
proposal paper titled, A Study of an Interstellar Object Explorer Mission, which was recently
published in the journal Planetary and Space Science.
And listeners are encouraged to also check out Dr. Stern's website at alanstern. space, where
you can also learn about Dr. Stern's latest books and publications and upcoming speaking
events. Of which there are many, and no doubt many more to come. [00:24:00] And stay tuned
for future episodes, in which I hope Dr.
Stern will be able to tell us about his most well known success, which is being the principal
investigator of the first mission to ever rendezvous with Pluto and Kuiper belt objects, New
Horizons.
In the meantime, thank you for listening. I'm Matt Williams, and this has been Stories from
Space.