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Matthew Golombek

August 9, 2022

Erik M. Conway,

Interviewer

Q: This is Erik Conway. I’m talking to Matt Golombek about the InSight mission’s landing site 

selection process, and I think it’s August 8th [2022].

Golombek: Ninth.

Q: It’s the 9th. Okay, it’s August 9th. See how out of date I am.

So, Matt, of course you’ve been our landing site guru at JPL now since Mars Pathfinder. 

Tell me how you got involved with the InSight mission process.

Golombek: So the PI of the mission is about my closest and earliest colleague at JPL. I actually

knew him before I got here, because his advisor when he was a graduate student was my postdoc

advisor, and we were working on similar things, namely the Tharsis region of Mars and how it 

got to be there. After I accepted the job here, after my postdoc, he was the first person I looked 

up. [laughs] And he was just finishing his postdoc or he was just starting it or something, I can’t 

remember, but we’re effectively the same age and we’ve been at JPL for within a few years of 

each other. I think he’s got a few years on me. So we’ve been close colleagues forever.

I was involved in all of the precursor proposals that went before InSight that were to do 

geophysical observatories, and mostly it was a personal thing to help them out with site 

selection, about where to put these things down and what to do with them. So there were at least 
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one or two proposals prior to InSight, and the first one was called GEMS. That was the first 

InSight proposal, which NASA insisted that the name get changed, because I guess there’d been 

some spacecraft already called GEMS.

So the deal we made, since this is mostly a geophysical mission and I’m a geologist, was 

that you still have to land the spacecraft, so you need to find a landing site, and I said, “Well, I 

can give you a landing site. You need a landing site, I’m your guy. [laughs] And let me be in 

charge of the geology portion of the mission, so let me lead the geology investigation, even 

though it’s rather ancillary to the whole project and what it does.”

So, yeah, I helped write the paragraph. There was one paragraph about landing sites in 

the GEMS proposal that got us to Phase A, and then I got pretty heavily involved in Phase A in 

terms of trying to determine where to land and how to minimize all the trade studies that 

typically happen if you have multiple landing sites in lots of different places. So there was a lot 

of legwork in the beginning of Phase A, and that culminated with a presentation at the Concept 

Study Report, which is the big review, the big giant NASA review where they come to, in this 

case, JPL, and everybody gets dressed up in jackets and ties, which normally, of course, I never 

do. [laughs] At Von Kármán, we all went up in front and sat. The landing site was one of those 

deals, because it’s a hot-button ticket. Everybody knows you have to land, and everybody has an 

opinion. [laughs] So I’ve been pretty much involved from the very beginning of the entire 

project.

Q: As you said, there’s one paragraph in the proposal, but it took a lot of legwork to get to that 

paragraph.
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Golombek: Well, the first paragraph was—so at the very beginning, there were initial constraints 

based on latitude and on elevation, and the elevation had to be below minus-2 kilometers, and the 

latitude had to be pretty close to the equator. I can’t remember exactly. Maybe 5 or 10 degrees 

north, and it was a pretty thin latitude band. If you just plot the elevations on Mars and you look, 

there’s not a lot of Mars that’s at that latitude range that’s below that elevation.

And the paragraph in the original GEMS proposal just said “We know about the 

constraints. Here’s an area called Elysium Planitia that meets those to first order.” And I think 

we even picked a latitude and longitude that was in that band and said, “Well, we’ll start looking 

here.” And that was it. There was nothing more about the landing site in the original GEMS 

proposal.

Now, when it was selected for a Phase A study, along with two other Discovery missions, 

then we got more serious and said, “Okay, let’s be specific. Where, in fact, can you?” And that’s 

where we started doing a lot more legwork. So we knew from Phoenix that it was not what you 

call a rock-tolerant landing system, okay? [laughs] It’s got three legs and it can accommodate 

anywhere from 35- to 45-centimeter-high rocks, which was better than Viking, but not as good 

as the MERs or Pathfinder, for sure. And we’d already gone through the Phoenix experience, 

where Phoenix started out and they said, “Well, we can land at Viking 2 with 20 percent rocks,” 

and by the end of the mission, they didn’t want any rocks anywhere. They wanted it like zero 

percent rocks. [laughs] They were so rock-hysterically-averse.

So we knew that rocks were an issue, and we knew from previous work with MER, areas 

that had high winds, which are never a good thing when you’re on a parachute, because your 

whole spacecraft and parachute accommodate that, and you have to get rid of those winds 

somehow. So we looked around, and there were three areas that met the latitude and elevation 
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constraints, and one was either at the very end of Valles Marineris, where it opens up and 

debouches into the Chryse Planitia, and that’s in canyons, and there’s a high rock abundance and 

you could never fit 130-kilometer ellipse in the canyon. It was just impossible.

Then there was an area near Isidis Planitia that also the remote sensing data suggested 

had high rock abundance and atmosphere storm tracks that went north and south across the 

equatorial region. So we said, “Well, that’s not so good.”

Then we looked at Elysium in a little more detail, and that was the area that eventually 

we zeroed in on.

An interesting tidbit was that in the very beginning of Phase A, some of the engineers at 

Lockheed Martin—because this is a Lockheed Martin spacecraft—felt that it could land at much 

higher elevations than the minus-2, and suggested that we actually go look in the Highlands for 

places to land. The JPL EDL engineers didn’t agree with that. It didn’t have enough margin for 

them, and there was a little bit of a fight going on between JPL and Lockheed Martin. [laughs]

But that didn’t stop us from go looking around the Highlands as well, and the trouble with the 

Highlands is there’s all these big craters and you can’t find a smooth, flat place that’s big enough 

to stick your ellipse that doesn’t have one of those craters in it. If it has a big crater, then it has 

slopes that are too high.

So we actually looked around the whole plant, but eventually we decided that there was 

this one area in western Elysium Planitia that had generally low rock abundance, met the 

elevation constraints, did not have high winds, and our initial mapping, we could put down 

about—I think we put down 16 sample ellipses and we looked at them and some of them had 

very low rock abundance in the remote sensing data, and so we made a decision right then, 

during Phase A, which is somewhat unusual, and said, “This is where we’re going to land.” So 
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that there’s only one place that we’re now designing the power system, everything on the 

spacecraft, the thermal system, the whole spacecraft is now being built for this one place, and we 

were betting that out of that 16, one of those ellipses—we only need one [laughs]—one of those 

ellipses would pan out.

And the other interesting aspect about InSight was there were no science constraints on 

the landing site. It was just land someplace, because—well, you had to deploy the instruments, 

which means you needed relatively low rock abundance, smooth and flat, because the 

instruments didn’t like rocks or slopes either, but, interestingly enough, you also wanted a place

that had broken-up regolith down to 5 meters, so that your mole would have a chance to dig 

down to it. So we had sort of these semi-science constraints which were through the instruments, 

but no other science constraints, “I want to land on the delta,” or, “I want to do this or that or the 

other.” No, just land, a place where you can put your instruments out, we’re going to be happy. 

So that simplified things. I didn’t have to talk to any scientist outside of myself. [laughs] It was 

just find a place that met the requirements, and that was the initial part.

We recognized one of the truly interesting aspects about the InSight selection was that the 

area that met the constraints was due south of MSL, Curiosity, and on the exact same orbit track 

as Odyssey and MRO, and that’s a problem because those are servicing MSL for telecon, and 

there are strict requirements about what you can do with a spacecraft on the same orbit that 

you’re servicing telecon. And it took almost a year to negotiate with MRO to figure out that we 

could take images of the landing site in high resolution, HiRISE dominantly because that’s the 

highest resolution, and CTX, because we hadn’t mapped these. We needed high-resolution 

images to be able to come to some idea of what the hazards were.
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And it was very—I mean, it literally took a year to work through all of Lockheed Martin

engineers about what could be done and what couldn’t, and they came up with this suite of 

requirements of if you were within so many degrees of off-nadir to MSL, you could go off a little 

bit more to image the area, because you have to roll the spacecraft target to camera.

What was even more interesting about this was that—so HiRISE took almost no pictures 

initially, because we had to wait for all of this to be worked out, but there was one human on the 

Earth who actually knew exactly how to do this, and his name was Mike Malin. He must have 

known something about how Lockheed does this, and without telling anybody, he got 90 percent 

coverage of that area in CTX before HiRISE ever really started imaging. [laughs]

Q: So he has to have just queued that stuff up and just didn’t tell anyone.

Golombek: We sent him a note. We said, “Here’s where we’re looking.” We gave him this big 

box that was, I don’t know, it was 10 degrees across, and he just started snapping pictures. We 

saw them. They were coming in. We’re looking on the MRO server, and here are all these 

perfect pictures. [laughs] And they weren’t even released to anybody yet, because Malin doesn’t 

release anything until he has to. [laughs]

So we had to get into the inner sanctum of MRO to see these images, and that turned out 

to be a huge boon, because having 6 meters per pixel, we could identify smooth and flat, even at 

that scale, areas that were better than other areas, and we got maybe a dozen HiRISE samples, 

just enough that targeted the different terrains, so we mapped out the whole area in terms of 

terrains at 6 meters per pixel, and then we got samples in HiRISE. You could quickly see which 
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terrains were smooth and flat and relatively rock-free, and which ones were not, and that was an 

enormous benefit, huge benefit that went around.

So I think by the time of the Concept Study Report, we probably had five or six HiRISE 

images, and we had already 90 percent CTX coverage, and that was enough to identify what we 

call the smooth plains, which was the super smooth and generally rock-free areas that we wound 

up settling on.

Then we did the standard thing of once a year, basically, for the development period, we 

had a down selection, so went from sixteen to four, which were preferentially in the northern part

in those smooth plains, and then we narrowed it down to maybe two or three, and then at the 

third year, we selected the site. I think we might have had a somewhat provisional site. And by 

the end, we had gotten, oh, probably 70 percent of the ellipse, 130-by-25, big chunk was almost 

full of HiRISE images, so we could map all the big rocks and see what the rock abundance was, 

we could measure the slopes, so we had a really good idea what things were going on. Then I 

guess there was Planetary Protection Review, that there’s no water there, which there wasn’t, and 

some other things like that.

So, yeah, it was a wild ride, and it was so much fun. InSight—you must know, having 

listened to people tell you about projects at JPL, that projects have personalities.

Q: Mm-hmm.

Golombek: And some projects are wonderful to work in and you feel like you’re appreciated and 

you’re working as part of a team and there’s real camaraderie, and it’s a wonderful experience, 

and InSight was that always. We always said that Bruce’s number one requirement was that there 
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be no jerkoffs on the team. [laughter] And somehow he selected everybody on the team, were 

really good people, and it was a pleasure to work on the project and with everyone there.

Q: That’s great, great. Sounds like it was a lot of fun.

Golombek: It was.

Q: So you kind of talked about the general process of site selection, but who else was involved? I 

know you didn’t have the big open community meetings you had on MSL and Mars 2020, but 

what did you have?

Golombek: Yeah. So we had the project science team, and because site selection was part of the 

development activity, at every major review there was a site selection presentation that showed 

where we were. The engineering, the Standing Review Board, was fully aware of where we were 

with site selection, so the entire engineering team knew what was happening, as well as the 

review board on the engineering side.

Then within the landing site selection itself, we had a Council of Terrains and a Council 

of Atmospheres, which I don’t think we quite called—I’m trying to think. With MER, we had 

the equivalent, but we didn’t call it that. And at Phoenix, I don’t think we had anything called 

that name, because it was sort of internal. But we named it Council of Terrains and a Council of 

Atmospheres for MSL. Devon Kipp, thought that was a way to make it sound like we were 

important, you know. [laughs]
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And we did the same selection of investigators from the science community via an open, 

competed, request for proposals to answer specific questions that were relevant to the selection, 

as we did for MSL, which had happened before, right? Is that right?

Q: It happened before InSight, yes.

Golombek: Yes, okay, it did. Yes. I was thinking back to Phoenix. Right. So MSL had a Council 

of Terrains and a Council of Atmospheres, so we did the same for InSight. The Council of 

Terrains included everyone that was working on specific data products that were important for 

the selection, so we had the rock mappers, we had the thermal inertia people looking at the 

thermophysical properties, we had the SHARAD people to look for subsurface reflections. That 

was important for planetary protection. So that was radar.

We had DEM producers, so the USGS at Flagstaff again produced the Digital Elevation 

Models from both the stereo HiRISE and CTX. We had an HRSC DEM producers from DLR in 

Germany, and they all formed the Council of Terrains, and that was co-chaired by myself and 

Devon Kipp, who was the lead engineer on the landing site side. So we had biweekly meetings 

and summarized what we were doing and making sure we were staying with the project schedule

and all that.

In addition, there was a Council of Atmospheres that was run by David Kass, so he was 

the chair, and there was a selection of five or six members of the atmospheric community to 

provide specific data products, so there were things like—InSight was an interesting mission

because it was arriving at dust storm season. So you don’t get to choose when you get to Mars, 

right? If you’re on a Type 1 or 2 trajectory, you get there at whatever time the orbit is with 
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respect to the Earth, and some of those times, it’s southern spring/summer, which is dust storm 

season, and you don’t have a choice. You’re going to arrive at that time. And when you’re 

planning the mission, you don’t know what the atmosphere’s going to be when you get there. 

You don’t know if it’s going to be clear. It’s going to be a raging dust storm, it’s going to be a 

regional dust storm or decaying dust storm.

So David had to characterize four atmospheres beforehand, and then as the spacecraft 

was on its way, we had MRO and Odyssey, and we’d be getting weekly updates about what the 

status of the atmosphere was, so that prior to arrival, we would select the correct one that we had 

already worked on and given pressure and temperature density curves to land in, and we would 

choose the EDL routine that would best match that atmosphere. So the atmosphere, if it’s a dust 

storm, you get more atmosphere higher up, but the area with maximum g-loads on the spacecraft 

during entry and descent is further down, and it affects the whole atmosphere, so the whole EDL 

trajectory changes a little bit, and you need to fine-tune the EDL algorithm to be expecting that.

Q: Right.

Golombek: So David had to characterize four different atmospheres, which hadn’t been done 

previously. We always knew that we were in low dust storm season or which part of the season, 

and you really only had to do one, but this one was interesting because you were arriving at dust 

storm season.

Q: So how did you choose these team members? Were they competed?
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Golombek: Yes. So we did it the same way we did for MSL. We had a Critical Data Products 

Initiative, which for MSL was funded by the Mars Program Office, and it made the case that 

these data products were critical for EDL, and we wrote an RFP, Request for Proposal, from JPL, 

not from NASA. We, of course, had to get NASA approval. And we wrote down all the things 

we wanted, and we were super specific. It’s not like a NASA AO that says “Learn about Mars.” 

Well, there’s a million ways to learn about Mars, okay? This was “We need Digital Elevation 

Maps at this resolution, at this scale,” yadda, yadda. I mean, it was super specific about what we 

needed.

Then they went through review. We had a full review panel, and the best one was 

selected, and then we went into negotiation with them for a specific contract to provide those 

things, and those members then became members of the Council of Atmospheres and the 

Council of Terrains.

Q: Okay. So was MSL the first time you’d competed those? Other times, you just picked who 

was going to do it?

Golombek: Yeah. So MSL was the first time we had an open call. MER, we just had members of 

the science team that helped out with certain aspects. Phoenix—oh, Phoenix had one. It probably

had a call too. I remember that.

Q: Oh, okay.
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Golombek: So there may have been a call there, but I don’t think we called it Council of Terrains

and Council of Atmospheres, but it was similar. Then by that time, we were in the swing of it. So 

MSL was like that. Then we’ve done it ever since. The interesting aspect is the Mars Program 

Office refused to pay for it because it was a Discovery mission.

Q: Right.

Golombek: It was using all Mars Program data, and there was an agreement, of course, to collect 

data from the Mars Program to help with InSight. [laughs] But, anyway, that’s politics.

Q: They wanted it to come out of the project budget.

Golombek: Yeah, and that’s what happened. Right. Then, of course, at some point you’re going 

to ask about what happened when we didn’t make the launch date, right?

Q: Yeah. [laughs] Well, yeah, sure. Why not now?

Golombek: [laughs] Since I brought it up.

Q: Yeah.
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Golombek: So we were on target, “we” now being the Council of Terrains and the Council of 

Atmospheres. We were ready. We selected in October, late September of ’16, I guess? Yes, ’16. 

Right. We landed in ’18, right? Yes. I think that’s right. Yeah, that’s right.

So we had selected the landing site. We’d gone through all the internal reviews. We had 

gone through an independent peer review that Gentry—Gentry’s reviewed every selection I’ve 

ever done. [laughs] We’re like comrades now. He knows me and I know him. [laughs] And we 

had a full external review of the landing site, and we went through planetary protection review in 

late October, and we were ready. We had selected.

The project declared—it was just about Christmas of that year—that the SEIS was not 

ready. It couldn’t keep a vacuum in the instrument, and they scrubbed the launch. I distinctly 

remember December was a quiet month, and we knew this was brewing and it might be 

happening, and I started to write the InSight landing site selection paper, the one I sent you, and 

I’m writing it and I’m going, “I don’t know if this is going to be a mission or not.” [laughs] A 

landing site selection, if you don’t have a mission, is an academic exercise, right? I don’t do 

academic landing site selections. [laughs] It’s got to be a real mission for me to get involved. I 

kept wondering, while I’m writing this massive paper, whether it was ever going to get submitted 

or not. [laughs]

So, anyway, I think it was just around—it was in December, and I don’t remember if it 

was at Christmas or right after or a little before, but they said, “We’re not ready. We can’t 

launch.” And I had just about a heart attack, because the place that we selected only had 

elevations that were slightly below minus-2.5 kilometers elevation, and there was nothing lower, 

and we hadn’t done any work on any other landing sites. And at that time, I didn’t know what the 

atmosphere was like for the next opportunity, which was 2018, right? Yes. So twenty-six months 
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later. And you arrive, because the atmospheric pressure changes by 25 percent, and you don’t get 

to choose which season you arrive at, you get whatever atmosphere Mars has at that time. You 

don’t get to pick it, right? If you did, you’d always pick the maximum atmosphere, and that 

would help your EDL a lot, right?

And I’m going, “We found a landing site that meets the constraints. I don’t have any 

place I know to go that’s a half a kilometer lower. There’s no win here. That’s only a loss. If 

there’s a change in the atmospheric pressure and if we need to search for someplace lower to 

give us more time for EDL, it means a whole new selection activity, and nobody wants that, 

including me.” [laughs] So for several weeks, I’m screaming. I was the person screaming about 

“Armageddon is coming!”

Well, it turned out that in 2016, we were just before the maximum atmospheric pressure,

and at 2018, we were on the other side of that maximum atmospheric pressure at almost exactly 

the same pressure as we were in ’16. So there was no change. We just said, “Okay, we’re done. 

We selected the site. We got nothing else to do.” Actually, we did continue to image the site with 

HiRISE. By the end of that two years, we mostly—yeah, we filled in as much of the ellipse as we 

could, we continued to map out the rocks, and then we did the full EDL after we’d done all that 

for the ’18 one. But that was just kind of sweeping up.

So, yeah, so that was a bit of an uncertain time. It turned out it only took the atmospheric

guys about a week to figure that out, and then it was like, okay, no change in the landing site, so 

we kept imaging it, and I think we retooled the EDL safety. We had very specific software. For 

any area that we mapped out, we had a hazard map that says what the probability of success 

would be if you landed at that particular part of the map, and you could then take a full Monte 
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Carlo simulation of all the places within that ellipse you might land, tally them up, and you get a 

single number, which is your probability of success for that ellipse.

And that, of course, was important for as you’re arriving at the planet, you never quite 

exactly hit the spot, right? You’re coming in at a particular place and you might be slightly off, 

and you have to figure out which TCM (Trajectory Correction Maneuver) to do to get as close as 

you can. You never quite exactly hit the center of the spot that you—the ellipse that you map 

beforehand, but usually by then the ellipse is smaller because you’re so much closer to the planet 

and you’re already starting to feel the gravity. So your ellipse is usually pretty close to where it 

is, but there’s this whole drill that occurs during approach, where you’re calculating out, you 

know, we hit the center point, we map it out, we calculate the numbers, we report it to the 

project, and that’s part of the decision tree for a TCM. So we did all that, yeah.

Q: We already mentioned that you didn’t have open community meetings. So why not?

Golombek: So, technically, for a PI-directed mission, the PI is the selector of the landing site.

Q: And not NASA.

Golombek: Not NASA. So Bruce actually, as the PI of InSight, had the—and part of that goes to 

the initial proposal and the Concept Study Report after Phase A was quite specific about where 

we were landing and what we were doing. So the acceptance of that proposal is effectively the 

acceptance of that site with the details of that. In reality, the process is no different than if it’s 

not. You still have to show it to Headquarters and explain your reasoning and so on and so forth, 
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but it was not as big an ordeal as what it typically is for a non-competed mission. Especially in 

those situations, you have full community input, you have the big open workshops and 

everybody gets their say, and NASA really looks at those carefully because they want to make 

sure that you haven’t not listened to anybody and you’ve done things completely aboveboard and 

in an open a way as possible. So none of that really mattered for InSight. We still report to 

Headquarters about our decision and why we selected it, but it was fairly pro forma. There 

wasn’t a whole lot more to it.

The Planetary Protection Review was more specific. That had to do with specific—you 

know, you could not go to an area with water or ice within 5 meters of the surface, and there 

were other very specific planetary protection requirements on the landing site. Those were done 

in 2015, so we didn’t have to redo them.

Q: I think you had four site selection team meetings, and the question I wrote was, what was the 

focus of each, or did they not really have focus?

Golombek: Each one had a specific—there was a goal at the end, and the meetings, again, they 

were more generally Council of Terrains- and project-specific, so they were much, much smaller, 

and for the most part, it was mostly the project listening to us; that is, the Council of Terrains

telling the project our conclusion.

So at the first one, we started out with sixteen. “Here’s the four that we wish to go 

forward with.” And that was interesting. That was done at the first science team meeting, which 

was at IPGP in Paris, and a big chunk of the science team showed up for it, and we had a full day 

of agenda. I remember I broke all the rules in France. I started a meeting at 8:30 in the morning, 
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which you don’t do in France, right? You don’t start anything before 9:00. [laughs] That was a 

big faux pas. But we went till 4:30 with presentations on all aspects of the mission, and all of 

these scientists were listening to us, and they never came back for another one. That was it. 

[laughs] It was like, “Okay, they know what they’re doing. Leave ‘em alone.” [laughs] So that 

was number one.

Number two was probably narrowing it down to maybe two, something like that. I can’t 

remember exactly. I’d have to go look at my notes again.

The third one was “Here’s pretty much the site we’re selecting.”

The fourth one must have been after—I’ve forgotten the details.

But, anyway, each one had a specific goal and end point. So the first one was dominantly 

to the science team. All the subsequent ones were to mostly to the project. Then the last one was 

to the peer review panel and the project. That was the official selection by the project. Again, 

that was done in probably September ’16, I think. Yeah.

Q: Somewhat broader question this time. So what new tools have become available for site 

selection, I mean, since you started with MPF or maybe you can start with MER. It doesn’t 

matter. But what would you say are kind of the new tools and what are the most significant?

Golombek: Yeah, that’s the interesting aspect, because with InSight, we figured that we knew 

what we were doing because we had done MSL, and MSL was the—you know, we mapped all 

the rocks, we mapped all the slopes, we had done everything that was humanly possible to do, 

and we thought that we had reached—or at least I personally thought that we knew all the tools 

and that there weren’t going to be any surprises. And what’s interesting is even if you do the 
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same task again a second time, there’s always surprises. [laughs] And the tools, you develop

newer tools that do the job better than you did it the first time.

So, an example, MSL had pretty much complete stereo HiRISE data and DEMs across 

the ellipse. There may have been one or two little areas that didn’t have it. But when we tried to 

put those DEMs together, they all had seams at the edge between one DEM and the other, and 

getting rid of those seams was a devil of a time, because each stereo pairs its own little universe

and you try to map them down on the same surface, but there’s always going to be slight tilts and 

adjustments. So we never really figured out a particularly good way to deal with that for MSL.

For InSight, we had almost complete coverage from CTX, which is the broader scale, and 

we just had samples at HiRISE, but the CTX joints had to be put together, and during MSL, we 

hadn’t actually developed a really good method to fully do the CTX DEM. So that was kind of 

developed a lot during InSight, and there we came up with a much more sophisticated way to 

actually merge those DEMs side by side so that you wouldn’t have these cliffs at the edge that 

would, of course, always trigger a crash in the spacecraft, because that’s like coming down on a 

cliff, which is never a good thing. So that was one thing.

We’d bin things in 150-by-150-meter boxes, so we had a slope distribution within that 

box and we had a rock distribution within that box and we calculated a probability of successive 

landing on that slope and rock distribution for each of those 150 meters throughout this big giant 

long ellipse, and that set the stage for—at some point, you may ask me about what we did for 

Perseverance in 2020—but that set the stage for a level of site selection specificity that no one 

had ever imaged or believed could be done.

So in that situation, is it okay if we go to that a little bit here? It’s a little bit off topic, so 

it’s kind of up to you.
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Q: Oh, sure.

Golombek: So for 2020, it’s landing in a very small circle which is—I thought it was 8 or 10

kilometers. It wasn’t even much of an ellipse; it was almost a circle. Let’s call it 10 kilometers. 

So it’s the smallest circle ever, and we had the ability to do what’s called TRN, Terrain Relative 

Navigation, so it can figure out where it’s coming down, and it had a divert capability that 

allowed it to go perpendicular to the entry direction by several hundred meters in either direction. 

So it could pick any place, either north or south—well, in this case, it would have been north, 

yeah, mostly north and south—from the entry trajectory for the projected landing point, and it 

could target the safest place it could find that it could divert to.

It had no hazard avoidance, so hazard avoidance we typically call where it’s seeing 

what’s down beneath it as it’s coming down, and it reacts to that and avoids bad things. TRN 

doesn’t do that. It takes a map that you already produced that says where the good things and the 

bad things are, and then it goes to the place that you said were good. Well, think about that for a 

second. Now the onus is on us geologists to tell them where the safest place is. It’s not just 

“Here’s the ellipse and here’s where you can move the whole ellipse around and you’re going to 

get this amalgam within it.” We need to find the safest places within that ellipse. And they 

targeted a ellipse that you never, ever would have targeted without TRN. There’s cliff faces in it! 

[laughs] You would never—that’s not smooth and flat and boring. It’s the antithesis of it.

So by the time we got to the end, we had to produce maps that would allow the spacecraft

to do TRN, in other words, the best registered and corrected base maps ever produced on Mars, 

so that TRN could do its job. Well, now, again, that’s on me, right? That’s me. And I need a 
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hazard map at meter scale that said every meter on that place was safe or not safe, and what 

percentage safe or not safe, and if I screwed up and said it was safe, and they land there and it’s 

not, then whose head’s gonna roll, right? It’s not the engineers doing hazard avoidance. It’s 

Golombek’s, because he didn’t get it right. [laughs]

So now we took this ellipse, and 90 percent of it sucked. Ninety percent of it had 10 

percent or more hazard. So we landed in 8 percent of that ellipse we said was safe, and we did 

horrendous things to figure out it was safe. We had individual interns looking at each spot 

[laughs] that didn’t have rock abundance, and all sorts of things that had never, ever been done 

before to get to that. I doubt we could have gotten there if we hadn’t had that InSight as that 

intermediate step beyond what we did for MSL. A lot of tools were the same. We had the rock 

detection software that we used to find the rocks and slopes and all those similar sorts of things, 

but it was taken to the nth degree and required a level of exactitude that no one had ever done 

before. So that was, yeah, truly beyond. And don’t even ask me about sample return, because

those ellipses are 120 meters! [laughs]

Q: Jeez. [laughs]

Golombek: A hundred and twenty meters, which you would say, “Oh, that’s great!” But now I 

need to find 120 meters and I need to find a place where you can’t even see the rocks in the 

HiRISE. They’re too small. [laughs] So, anyway, it’s not getting easier.

Q: No, despite the fact that tool—so the tool development is actually making things harder to 

some degree.
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Golombek: Or the requirements, and pushing the requirements to this nth degree, is making 

things more difficult. So I’d say a lot of the basic tools haven’t changed all that much, so 

stereogrammetry, getting stereo DEMs from them, we have state of the art, we know how to do 

that. We do it pretty well. There’s a few tweaks here and there, some of the things about getting 

the boundary of the DEMs together and smoothing those out. The rock abundance, we did all 

sorts of things beyond what we had done previously to try to make sure that there were no rocks 

of any size, so we wound up running it and not even knowing if they were real rocks. We just 

wanted places where there were no detections anywhere by any of them, even if we weren’t sure 

about the detections. [laughs] It kind of pushes you to that. So a lot of tools were pretty similar, 

but sort of pushing it to the nth degree made it—you had to be more careful in what you thought 

you knew and what you didn’t know, in terms of the data.

Q: You had, I guess, one new tool, is the orbiting radars. How did those factor into this? I guess 

there are radars in MRO and Mars Express, right?

Golombek: Yeah. So Mars Express didn’t help much. That’s mostly far deeper.

Q: Oh, I see. Okay.

Golombek: Yeah. So we were looking at SHARAD, which is the shallow. SHARAD is not 

actually designed for looking at the near surface. It’s actually better looking at tens to hundreds 

of meters below the surface. But there was a planetary protection requirement that there be no 
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subsurface interfaces that—I guess they were concerned about trapping water at shallow levels, 

and we thought SHARAD was our best way to see if there were any subsurface reflectors that 

could be of concern, and we used it mostly—we did it for two reasons. One is, could we get any 

idea about what the physical materials were in the top few meters, and to see if there was any 

evidence of subsurface reflectors that might influence the planetary protection.

And we also had them look at the—so we had a C-band radar on InSight, and we wanted 

to look at the Earth-based radar, because it had a wavelength that was near the C-band, just to 

make sure we had a radar reflective surface. So we had both of those in that contract for the radar 

investigation, and that turned out quite well. Those guys did a smash-up job and wrote a bunch 

of papers. And they saw a few reflectors, but not much, so it strengthened our case for the 

planetary protection, and it gave us just a wee bit more—we were more certain that we would 

have a radar reflective surface. There was nothing unusual about the radar properties. So you 

clearly want to have the radar detector working on your spacecraft as you’re coming down. 

[laughs]

Q: Yeah, yeah. We’re about out of time. Is there anything important that we should talk about?

Golombek: You got most of it, yeah.

Q: Okay, great. Thanks for your time.
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Golombek: Always, and continue to do all that good stuff you do, because I think it’s really good 

that JPL has somebody like you, because things disappear when you get done with them, and 

they’re gone. People are gone.

Q: Yeah, corporate knowledge vanishes.

Golombek: Yeah, yeah, yeah.

Q: All right. Great to talk to you, Matt. Take care.

[End of interview]