Playing Acornsoft Planetoid in 2017 compared to 1995-1996

On this page:

On separate pages:

defender, what planetoid emulates, mostly acornsoft planetoid and defender
acornsoft defender instructions acornsoft planetoid instructions
Note that the score for a bomber is actually 200 points, not 150 as per the instructions...


In April 2017, having some more time to spend on hobbies I decided to play some games on my BBC micro. I saw's high score competiton tried the current game, Galactic firebird. I got to 27K or so, and others had scored 33k+, but I didn't want to try further as the game just didn't grab me and what I really disliked is the too long pause between dying and playing again, but still I wondered if my skills were now rubbish or that I just needed a bit more practice on that game. Well, to compare then and now, I tried one of my favourites, Planetoid. I could have tried Fortress, at which I got to 268000 and 248000 in 1986, but I am sure that those scores are almost impossible to improve on as I played perfectly for the highest score. I had to even shoot a few barrels of fuel that are hard to get to (behind walls), and for a higher score I would need to shoot a few of the barrels that are almost impossible to get to (also behind walls but closer to them and/or with enemy planes, not sure) because fuel depletes faster each time you go through the course. So Planetoid it was, after not having played it for almost 21 years. My high score in April 1996 was 888150, what would I get to now? First 3 days:

Tried Galactic Firebird again and got to 33850 which was OK but not great, but I couldn't get myself to put in more effort. So back to Planetoid.

Over the next weeks I played Planetoid from time to time, with my score getting higher, and the realisation of how much high scores depend on subtleties (to not get killed, to not kill your last man, how to deal with certain situations) grew. It just takes time to master them and to apply them. Also you hit a almost-wall until you get to wave 32, you need to become good enough to reach that (you will get there with about 520k points) and of course have enough lives and smart bombs left over to continue, as at this point the shoot-speed of aliens wraps around making it manageable again, and you can continue (but aliens become faster all the time and suicidally run into you, so it doesn't get easy! The swarmers' speed is a problem at high scores and even worse are the baiters/cruisers). Comparing my scores with those from 1995-1996 (I wrote down all my high score improvements with dates) showed that I progress much faster than then, and I felt that I could definitely improve on my 888150 high score. At the time I felt more than 900k was possible and I wanted to get 1M+, but it was frustrating when the speed of a lander is so high that they take the last man up a very long way in short time and if you get killed often a lander still got to the top resulting in a mutant fest. Also, other things took my time from mid 1996 on. Well, I will try it this year... Shoot speed should, at a bit more than 1M, reach the maximum again so it will be difficult.

I made some videos, first with S5, then with S2 which is a bit blurry for some reason (in short tests recording Planetoid the video was better than of the S5 in low resolution)


In a bit of night play on 6-7 June 2017 I got 2 improvements for 2017: 812450 and 857300 (end of wave 50, the maximum tab bombs/lives I got to was 39/28). The large number of tab bombs meant a good buffer for situations such as not keeping the last man alive, as happened twice in the 857k game, in wave 47 most notably so a bit more than 2 waves in a mutant fest. I also wasted a few smart bombs accidentally pressing TAB twice (first time that ever happened to me during playing Planetoid, curiously). The score is very close to my 1996 high score, so my skills are definitely not worse than in 1996. I know for sure now that I can improve on my 1996 high score by a large margin because in both 800k+ games I was testing tactics and not playing optimally at all.

A while ago for the high score competition on I also briefly tried Zalaga for several games and within a short time I got to just under 150k, whereas in 1995/1996 my high score was 154k. So, very close but I didn't try to improve on it as it is such a boring repetitive game, and I know I felt the same in 1996, which means that I didn't do much effort for a high score then, just as I didn't do much effort this year, and thus any comparison would likely not tell anything about the ability to play computer games now vs. then... (that fact was a big part of the reason why I didn't continue to play this game further to get a higher score in that competition)

2017-7-24: I think I can score 1M+ with the current strategy, but I have been analysing what I need to do to score much higher which would likely be needed if those scores of 2.8M and 3.1M are real. I've tested a new strategy, so far not succesful ;-) If no result soon then I will go for 1M+ with the old strategy.

Comparison with Alligata's Guardian, the original Williams Defender arcade game and a few more BBC micro versions

Alligata's Guardian: Interestingly the intro screen says 'Defender' :) This is more accurate in emulating the Arcade game, at least in movement patterns of the bombers, baiters and swarmers, than Planetoid. What is bad is the lack of colours. This makes it harder to play, esp. the radar is hard to read, and this along with the very poor sound (the game looks to use a single sound channel for use on the Acorn Electron, which means a new sound cuts off an already playing one. This game seems to have been released only for the Electron which makes sense as anyone with a BBC micro would likely have Planetoid already), are 2 of the reasons why I don't like Guardian, but there is more such as the too long continuing of motion (too slow deceleration) and the too long lifetime of bullets, which makes reversal to make them go off-screen (= gone) and then back, almost a necessity for playing, all the time, instead of as in Planetoid, a method to be used most of all in extreme situations. Another issue is that there are too many landers appearing at a time (8 instead of 5) which makes it a quite different game to play. With Guardian you need to hammer the RETURN key all the time to kill all of them off (before the baiters arrive). Bombers and baiters behave more like the arcade game, with random up/down direction changes of the bombers, and the baiters moving rather less predictably than in Planetoid. This takes getting used to, you need a different approach. Shooting aliens is rather easier in Guardian, often with the bombers in Planetoid for example, hits don't register, in Planetoid collision detection is colour based rather than sprite shape based, I think. This shows also in the modified version that is around called "Super defender", where landers are very hard to kill because of this... I've not played Guardian long enough to see a wrap-around in shoot speed or alien movement speed (as happens in Planetoid at high levels), I played it only long enough to beat the highest score that I saw on and got to 389050, it seemed to get faster all the time, what will happen in higher waves?

Micro power's Gauntlet: I played it only briefly, it is almost but not quite Defender, with different shapes of aliens, different scoring and the bombers fire bstards at you ;) I could describe it better but I'd need to play it more and just playing it briefly I just don't like it, it's like playing in molasses. I think it's caused by the low speed and almost instant deceleration. Speed and deceleration are perfect in Planetoid. In Guardian deceleration is too slow.

Acornsoft Planetoid: This game gets harder all the time, but at wave 32 one part of the game gets back to easy. Why wave 32? Well, think about 8 bit values... At this point a wrap-around occurs of shoot speed, bullets are nearly motionless (and so you can deduce that likely 8 gets added to the bullet speed each wave and that the start speed was about 8, or 7 gets added each wave and start speed was ca. 39, or, with an addition of 6 each wave start value was 64, etc. I will check my disassembly to see which it is, though from playing it doesn't feel at all as if shot speed gets doubled after wave 1 so likely it's the 2nd or 3rd; There is some variation in shot speed but mostly up-down (more on this will come in the tactics section). So when you get to wave 32 you've got a reprieve from the unmanageable speed at which aliens shoot at you at around wave 28-31 (it already gets quite hard from wave 25), but the movement of aliens still gets faster all the time and they don't care about colliding with you, thus killing you! Baiters at I would estimate around 800k points (very rough estimate as I tend to avoid them appearing/analysing them at the lower waves as mostly they just kill me ;), have a wrap-around in move-speed, and you can easily shoot them again... Although never really easy as they are so thin. In general hitting aliens is harder in Planetoid than in Guardian and Williams Defender. Mutants at 800k+ are almost unmanageable, because they are so fast... (landers too but these are manageable as they are not homing in on you). When will the speed of landers and mutants wrap around to near 0? I should examine my disassembly...

Acornsoft Defender: There is an earlier version of Acornsoft's Planetoid called "Defender", which I was told long ago has some bugs. On youtube I saw a comment that if you end the wave with 10 men lifted, next wave you will end up with 256 men and no aliens. This sounds fishy of course, as the number of men is likely stored in a byte so you would never get 256 of them. And when I tested to see if anything interesting happens: Nothing interesting happens, the next wave continues normally. So what are the actual bugs? I will try to play this early version more in July or August when I return from a long trip and then I suppose I will find the bugs...

Other versions of Acornsoft Defender/Planetoid: There are a few modified versions which are not offical releases, such as "Modified Defender" and "Super Defender". I prefer Planetoid, I mentioned one issue above, I will try them again soon and give my more verbose verdict...

Willams Defender (the original arcade game): This is normally limited to a difficulty that stays at that of wave 15, so if you master the game at that level, then you can go on forever... Movement of bombers and baiters is very different in Planetoid than in Defender, and baiters appear a lot more quickly with less than 4 aliens remaining. I only played Defender briefly when "Williams arcade classics" came out, I think 1996? Maybe I will try it a bit more this year.

Planetoid tactics

Note that I don't read tactics by others, I try to figure it out myself, this is part ot the fun of playing and trying to get a higher score, it's not just an action game, but it's about developing tactics, you need to analyse how to improve! So I recommend not reading my tactics, but if you want to know more, see this page.

High score list from the web, old magazines, and my own scores, and "are those scores real?"

I collected highscores from some magazines, the site and my own scores, and other sources such as scores from's competitions and perhaps I will go through a few other magazines to see if they have high score lists. Any suggestions for magazines? Even better would be references of which issues contain score lists!
Also I discuss the scores are of some games that interest me, on how likely these high scores are real, and whether some scores were likely done on an Electron or even an Electron version on a BBC micro (or BBC version on an Electron!). See this page.

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