Reference / Paper · 1978

Moon Landing Game

A five-page construction article from Practical Electronics (November 1978) describing a small analog computer game that simulates a lunar module descent. The circuit uses operational amplifiers to model the physics of the lander — computing velocity, altitude, and fuel consumption in real time — while the player controls the rocket motor to achieve a soft landing. The article covers the schematic, component list, PCB layout, panel wiring, and calibration procedure.

Manufacturer: Practical Electronics
Author: A. Russell
Year: 1978
Type: Reference / Paper
Language: English
Learning track: specific applications
Pages: 5
Credit: Practical Electronics, November 1978

Practical Electronics
analog computer
game
op-amp
educational project

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Moon Landing Game

MOON LANDENG GAME T the controls of this gare you san land your own Pr scacs ship on the Moon:and test your. skill and timing by ‘guiding the rocket to. a safe landing before the fuel rungs Gut: Moon Landing @ essentially « bard wired analogue computer which simulates a@pproximately the Syshamics ‘of a Space “craft ianding on the Moosn. Additional citcufiry monitors the computer and awitches.off the rocket moter when-the fie! runs out, indicates when the. craft has landed, and: shows when & safe danding velocity ig achieved. Playingthe Mooi €ending game sivas chitdren a feek.-for. the concepts of distaniés, velocity. and accelerstion ant tHe Telationships betwean then. Thus aswell as being tun to play it also has an educational walue CONTROLLED DESCENT You are pilot of the first British expedition to the Moon. At one minute before touchdown the flight control computer blows a fuse, leaving you to land under manual control. There is a lever to control rocket motor thrust and a meter which can be switched to read velocity, height or fuel reserves. Your object is to achieve touchdown at a safe landing speed. Two lights are provided; one tells you that you have landed and the other indicates whether or not the touchdown was at a safe velocity. Therefore when both lights are on together you have completed a successful landing. A “Panic” button is provided. In the event of fuel running out before landing (because of a bit of ham fisted driving on the part of the pilot) it will divert the contents of the medicinal whisky tank into the rocket fuel tanks, giving an extra 15 per cent fuel. SCHEMATIC The analogue computer in Moon Landing represents a simplified view of a space craft landing on the Moon. No account is taken of the changing mass of the rocket as it burns fuel or changing gravitational attraction, etcetera. A schematic diagram of the game is shown in Fig. 1. It is not intended to explain in detail the theoretical background of integral calculus and analogue computers. Those interested in finding out more could start by lb the “Analogue Computer” series currently running. In Fig. 1, the value of thrust selected by the pilot is fed into Integrator 1 which calculates the total quantity of fuel used. When fuel runs out a level detector switches off the thrust. A “Panic”: switch feeds more fuel into the fuel tank when it is pressed. Thrust from the rocket engines is added to Moon gravity to give total acceleration acting on the ship. Integrator 2 calculates the resulting velocity and a level switch lights the ‘Safe Landing Velocity’ light when the downward velocity of the space craft falls below a certain value. Velocity is integrated by Integrator 3 to give space craft height and another level switch detects when this is zero to light the “Surface Contact” light. CIRCUIT The circuit diagram is shown in Fig. 2. Switch S2 has three positions. In the “Off” position power is disconnected THRUST kr DETECTS MOON FUEL seve 5 fe) = =. 33 = GRAVITY RUNOUT SWITCH i MOON LANDING panic button @ thrust safe surface landing contact velocity @ & fuel velocity height Control panel layout from the circuit. In the “Reset” position capacitors in each integrator are charged to +5-1V to fill the fuel tanks (Integrator 1), give the rocket a large downward velocity (Integrator 2) and set the initial height above the Moon (Integrator 3). When S2 is moved into the “Go” position the analogue computer starts its calculation. Slider pot VR1 (‘Thrust’) controls the voltage across R4. This voltage is fed into Integrator 1 (I1C1) through R3. Output voltage of IC1 falls at a rate determined by the voltage across R4 (the “Thrust” setting) until point A goes sufficiently negative to forward FUEL LEFT f THRUST ~ PANIC WHISKY TANK Fig. 1. Practical Electronics © November 1978 ACCELERATION > VELOCITY DETECTS SAFE LEVEL ° LEVEL LANDING VELOCITY§ SWITCH SWITCH DETECTS CONTACT WITH MOON SURFACE SAFE LANDING VELOCITY SURFACE CONTACT Schematic diagram 1139 \ ee meal eevee oc — et eafeaeoe é . ?* ‘¢ * “ o > e . * * i 5 ¥ a eee fe ee toni, * @ee eee ee ee eee eennes eeenee ee oe oasesee —(b-— o> eevee eee ew eeee eeetece eee eee awe Seer ee even enewes ee ee 8 6 ate Pee eevee eee eo Ce eee eee ee eee. ce eee eee ee @eeceeene eevee - ee ee eee eevee eee veeevesee eee ee eevee ee oeseve #eeeeneve eeeevecue ee eeveseme eee e ¢ # of — eee eens ee ee is ee #eeeoevsverne Seee¢eovevnve eee eeeeene @eeeesestases HEIGHT Oe ORIGINAL METER CALIBRATION Fig. 5. Rescaling an existing milliammeter CONSTRUCTION The Veroboard layout of the Moon Landing circuit is shown in Fig. 3 and should present no constructional diffi- culties. Connections between the Veroboard circuit and the switches, |.e.d.s, etc. are shown in Fig. 4. These components are all mounted on the front panel. A plastic sandwich box was used to house the complete game and the layout chosen for the front panel controls is shown in the photograph. CALIBRATION The 1mA meter ME1 requires a new scale. Fig. 5 shows the relationship between the original O-1mA calibration and the new one for fuel, velocity and height. The new scale may be drawn on plain white paper, cut to shape and glued into position. Take great care not to damage the meter move- ment while taking it apart. Use the zero adjusting screw on the meter to set the poin- ter at zero on the velocity scale with the power off. Adjust VR2 to make the initial values (immediately after Reset’) of fuel, velocity and height agree with the new scale. The meter is now calibrated and landing is for “go”. 1142 Practical Electronics | November 1978