GC SF Sp WH BV YL BT CP SA CB CC Back to puzzle


Mars Rover

by Brent Holman

This is a bit of a crossword/logic hybrid, and figuring out the right order in which to tackle things is a big part of the challenge. Here’s one possible way to go about things…

1. Looking through the log transcripts, the 7th one should stand out as a likely introduction, and the 4th one should stand out as coming later than at least some of the others (“now that the crater is fully mapped out” should come after the crater is fully mapped out, presumably). The other 6 are jumbled together, so it’s a matter of figuring out an ordering that works logically. Log #7 is a good place to start.

2. Per log #7, you can fill the six corners of the hex grid: A through F, going clockwise from the top. The text here says that there will be seven outings in the NAV, so presumably the audio files will start to come into play from here on out. Log #6 mentions “outing one,” so let’s jump to that one next.

3. Per log #6, you can fill the perimeter of the hex grid (one letter per small hexagon). Don’t worry about the audio files yet, just think of it more like a crossword at this point. Going counter-clockwise from the top, you can fill in ABRAMS, FRANCE, ENGLAND, DENVER, CANADA, and BONANZA along the outer edges of the grid. This is clued more or less directly; you just need to parse the references to the shows or songs in question. E.g., those countries come from the Animaniacs "Nations of the World" song. Remember that each word begins in a corner and proceeds toward the next one around the perimeter. You know to go counter-clockwise so ENGLAND and BONANZA will fit in the grid.

4. At this point, we can start to investigate the audio files. According to the flavor text, there should be an audio file associated with each outing in the NAV. So there must be a file that goes with the perimeter circuit. The audio files contain only three different sounds, so we need to figure out what those sounds represent. In fact, the sounds themselves help a lot: the one you hear most often represents moving forward one space, while the other two represent turning left (higher pitch) or right (lower pitch). But even if the sounds don’t spark any ideas, the patterns themselves can be used to reach the right conclusion. The second-longest file contains a very regular pattern: 6 of sound A, 1 of sound B, repeated several more times. This corresponds to the perimeter circuit, with sound A being “go forward” and sound B being “turn left.”

5. For the remainder of the video logs, it becomes a matter of matching them with the appropriate sound files and then placing the appropriate phrases into the grid accordingly. Getting started might feel tricky at first, but you’ll notice that the first log mentions a trip straight across the hexagon from corner to corner. If you figure out the phrase BALLROOM DANCE, there’s only one way that that can fit in the grid: starting at the NE corner (B) and proceeding to the SW corner (E), as indicated by the blue letters in the solution grid. This effectively splits the grid in half.

6. After that, you might notice that the longest sound file is again just a bunch of A (forward) and B (turn left) sounds, making a loop or a spiral. The last log transcript mentions spiraling and contains a very long phrase, so let’s figure those go together. Sure enough, the number of “forward” sounds in the audio file matches the number of letters in the phrase (not counting the first letter, since that’s the starting position). If you map out the turns, you’ll see that it makes a shape that matches the area bounded by the perimeter and BALLROOM DANCE. However, we don’t know if it goes above the blue line or below it. So we’ll put a pin in that for now.

7. At this point we can match log transcripts to audio files pretty easily with one simple trick: the number of times you hear the “forward” sound is equal to one less than the number of letters in the target phrase of the transcript. This is due to the fact that we’re dropping one letter in each hex, and have to move forward to get to the next one. With that in mind, we can map out the NAV paths and add letters to them, sort of like creating jigsaw puzzle pieces that will fit together.

8. The next entry that can fit into the grid unambiguously is log #3. The missing words from the song (“Open Arms” by Journey) are LIVING ALONE. The only sound file with 10 “forward” sounds is just a straight shot with no turns at all. The only place in the grid where that can fit is directly above BALLROOM DANCE, as seen in the green lettering. (Keep in mind that overlapping letters is allowed, as we saw in the very first outing: the perimeter circuit had overlaps on the D and the A corners.)

9. Now that LIVING ALONE has been placed, we know that the long phrase from the NASA transmission has to go below the BALLROOM DANCE line instead of above it. The brown letters and yellow line show how that fits in.

10. From there, the final three entries can be placed in a similar manner. Two of them are disco songs as heard in the background of their audio files. “Don’t Leave Me This Way” can only fit in the grid in one way, and “I Will Survive” follow suit after that. The final entry, DISCO MUSIC, is just a tight circle of letters near the top of the hex grid, as seen in purple.

11. “Now that the crater is fully mapped out,” we can move on to the next step: the hydro stations. Log #5 mentions that there are 19 stations in total, and that each one covers what amounts to a medium-sized hexagon made of seven smaller hexagons (one central hex and the six surrounding it). It also mentions that two of the stations should be placed at the head and tail of a “beast” hiding in the crater. Wait, what?

12. If you look at the grid like a word search, you can find a MINOTAUR hiding near the center (bold italic letters, red line). There’s our beast! So we can start by placing hydro stations at the M and the R of MINOTAUR and marking the surrounding spaces as well. (Those spaces have been marked as gray and light gray, respectively.) The first two of our 19 stations have been placed, and now it’s a matter of finding the placement pattern for the rest of the stations that gives us the highest coverage without any overlap.

13. This might feel like a daunting problem at first, but it’s actually pretty easy to just dive in and experiment. We know we want maximum coverage, so it makes sense to guess that we’ll more or less tile the plane with our seven-hex clusters. There are really only two ways to do that, and one of the two works much, much better in terms of covering spaces along the outer edge of the grid. As an illustration, let’s look at the second column of the grid (SSIWINCN). We can place a hydro station on the first S, but that leaves single-hex gaps next to the existing station that we’ll never be able to fill. So what about the second S? That one nestles up against the existing station very nicely, and even covers the corner. Looks good! But if you keep nestling up against the existing stations, you’ll quickly find that this pattern doesn’t give us great coverage overall. Finally, try putting a station at the first I in that column, as shown in blue. It also nestles up against the existing station. But the difference there is that if you keep extending the pattern by placing stations that nestle up against the existing ones, you end up covering almost everything in the grid (missing only the six corners) with 19 stations. Looks like we have our winner!

14. Now, looking at the 19 locations of the hydro stations, we can read off our answer. What is causing the problems with our communications and our terraforming efforts? MINIMAL CLOUD STORAGE.

Filled-in Grid, Reference

[hex grid with lines and letters in color]
Log Aud
Entry Grid Description
1 0:43 BALLROOM DANCE blue letters
2 1:06 DISCO MUSIC orange line
3 0:35 LIVING ALONE green letters
4 (n/a) (n/a) (second grid)
5 1:29 I WILL SURVIVE blue line
2:04 DON’T LEAVE ME THIS WAY green line
black letters
7 (n/a) (n/a) (n/a)
yellow line

Hydro Stations

[hex grid with hydro stations]