Mission profiles of early U.S. lunar probes

Sven Grahn


At the end of 1957 and early months of 1958 many persons and organizations in the U.S.A. were jockeying for positions to get the task of answering the "Sputnik challenge". The pressure from politicians in the U.S. executive branch and in Congress on those responsible for missiles and space development to quickly come up with significant space exploits was intense. The Air Force Ballistic Missile Division in Los Angeles (with the Space Technology Laboratories as their engineering organization) under Brigadier General Bernard Schriever was one organization that thought it had the necessary know-how and clout to do the job. The same was true for the U.S. Army Ballistic Missile Agency under General Medaris and with Wernher von Braun in charge of its engineering organisation in Huntsville, Alabama.

Thus, the White House announced on 27 March 1958 that it had approved a program "to determine our capability of exploring space in the vicinity of the moon and to obtain useful data concerning the moon". The program was announced by Defense Secretary Neil H McElroy. The Air Force Ballistic Missile Division in Los Angeles was assigned a program of three lunar probes using a "Thor-Vanguard" system with "a third stage to be developed". The Army Ballistic Missile Agency in Huntsville, Alabama was authorized to "undertake one and possibly two lunar probes" using modified Jupiter-C rockets. Overall responsibility for the lunar probe launches was assigned to the Defense Department's Advanced Research Projects Agency (ARPA).

The Air Force project had its roots in the "Able project" which was probably designed to provide a rocket that could test  re-entry vehicle (RV) technology for the ICBM that had not yet been flown successfully. To achieve the speeds necessary to test a reasonably sized RV the USAF and its contractor the Space Technology Labs used a Thor IRBM with the second stage of the Vanguard as the upper stage (see picture on the right of second stages being prepared). This combination was test flown three times in 1958, the first time less than a month after the White House announcement and the last less than a  month before the first lunar probe attempt. (Launch dates for the Thor-Able 0 rocket are: 23 April, 9 July and 23 July 1958).

When NASA was formed in October of 1958, all military space research projects run by the military organisations were transferred to it. This included the four remaining flights in McElroy's (ARPA's) origonal plan and the follow-on space probes planned by the USAF. This plan included a plan to launch two probes (weighing 169 kg) to Venus in the launch window opening in June 1959 followed by a lunar orbit mission. However, after the Soviet success with Luna 1 the plans were changed to instead launch the follow-on provbes to lunar orbit in the hope of beating the Soviet Union to this goal. This follow-on Pioneer program used the Atlas-Able rocket and even before the first flight the goal of photographing the far side of the Moon was snatched by the Soviet union. Howevber, the first probe did carry a camera - it was too late to change the plans. howveer, the two following oprobes did not carry a camera, but instead more radiation monitoring instruments. However, the goal of achieving lunar orbit before the Soviet union could still be achieved.

List of launches

The two tables below list the known launches in the first three U.S series of lunar probes. The first table gives technical details, while the second givesa dates and flight results as well as lunar coordinates. 

L/V                 Instrumentation Propulsion Electr. power RF System                                      

TV camera,
radiation detectors,

Falcon motor for
lunar orbit injection
Verniers for trajectory  adjustment

Batteries 108.09 MHz, 50 W, TV
108.06 MHz, 0.3 W, TM
114.81375 MHz, TC




108.09 MHz, 50 W, TV
108.06 MHz, 0.3 W, TM
114.81375 MHz, TC





108.09 MHz, 50 W, TV
108.09 MHz, 0.1 W, TM
108.06 MHz, 0.3 W, TM
114.81375 MHz, TC

Juno-2 Radiation detectors



960.05 MHz TM
Juno-2 Radiation detectors



960.05 MHz TM
Atlas-Able TV camera,  magnetometers, radiation detectors 2 hydrazine engines.
66 cm tank
in 1 m dia S/C.
4 solar panels

378.21 MHz TM 64 bps
401.85 MHz TC

Atlas-Able No TV camera



378.21 MHz TM 64 bps
401.85 MHz TC
Atlas-Able No TV camera



378.21 MHz TM 64 bps
401.85 MHz TC

A lunar age constraint?

The first three U.S. probes aimed at the Moon carried TV cameras to take pictures of the Moon's far side and therefore the lunar age at arrival should be be near zero, i.e. at New Moon. This means that the launch time should be a few days before New Moon, i.e. at Lunar age near 27 days.. This is indeed true for Pioneer-1 and -2, but not for Pioneer-0, the failed launch attempt on 17 August 1958. Therefore another constraint must be taken into consideration, namely the lunar declination at arrival. Since the launches were carried out by a direct ascent to the translunar trajectory from a site in the northern hemisphere the location of the moon had to be in the southern part of the celestial sphere, i.e. the declination of the Moon needed to be negative. (This is the same launch constraint as that of Soviet lunar probes). When the Pioneer-3 probe was launched in December 1958 the launch constraint was not not lunar age, but negative lunar declination. However, during the late fall of 1958 the Moon was a t its lowest declination near New Moon, so the launch of Pioneer-3 is very close to those of Pioneer-1 and -2 in the Age/launch time diagram below.
The P-3 probe launch in November 1959 again carried a TV camera for taking pictures of the Moon and the lunar age at its launch was very close to that of Pioneer-2. In the fall of 1960 when the P-30 and P-31 probes were launched the Moon was again near its lowest declination close to New Moon.All these factors have led to, by pure co-incidence that the early U.S. launches to the Moon are much more clumped together in the lanuch Time/age diagram that the Soviet launches to the Moon in the same period.The arrival times are based on a flight time for Pioneer 0-2 to the Moon of (57.5 hours until retro-firing) 62 hours to lunar orbit. The planned flight time to the Moon for Pioneer-3 and -4 was 34 hours. It seems that the flight time for the Atlas-Able probes was also 62 hours ( 1). 
Name Date
at launch
L/V Notes
arrival time
Age, Decl.Phase
at arrival
Decl. at 
Pioneer-0 17 Aug 1958
Thor-Able Exploded at T+77 sec  20 Aug 0218 UT
5.6, 212
Pioneer-1 11 Oct 1958
Thor-Able Too low speed. Hmax=110 000 km 13 Oct 2300 UT
1.3, 214
Pioneer-2 8 Nov 1958
Thor-Able Third stage did not ignite 10 Nov 2130 UT
29.1, 221
Pioneer-3 6 Dec 1958
Juno-2 Too low speed. Hmax=102 000 km 7 Dec 1545 UT
26.1, 211
Pioneer-4 3 Mar 1959
Juno-2 Missed Moon with 60 000 km 4 Mar 1511 UT
24.8, 286
P-3 26 Nov 1959
Atlas-Able Shroud splits at T+70 sec.  28 Nov 2126 UT
27.9, 224
P-30 25 Sep 1960
Atlas-Able Second stage fails to ignite 28 Sep 0513 UT
7.6, 278
P-31 15 Dec 1960
Atlas-Able Explodes shortly after launch. 18 Dec 2240 UT
0.5, 274

The figure below shows the relationship between launch time and lunar age for the flights in the table above. The blue line has been computed as outlined in
"How to compute the launch time of a lunar probe"    using an inclination of 33o and a flight time of 2.5 days. The fact that an inclination slightly above 30 degrees was used can be gleaned from a plot of the planned Pioneer-4 trajectory published by NASA.
The flight time must be either 0.5, 1.5 or 2.5 days to permit viewing of the lunar approach from the United States, in particular from the Goldstone station in California. A flight time to the Moon of only 0.5 days would require a very high energy trajectory with an injection velocity of 13.7 km/s, clearly an impossible figure! Therefore the shortest flight time to the Moon was 1.5 days, which was what was intended for Pioneer-3 and -4. All other probes aimed at 2.5 days flights time, i.e a period of about 60 hours.

A lunar declination constraint?

Just as for the early Soviet lunar probes the declination of the Moon at arrival was always negative. We can use the declination phase plotting method developed by Richard S Flagg (See "Mission profiles of 7K-L1 flights" ) and plot the early Pioneer missions in the declination phase/Age diagram. From the figure below it is again evident that the declination of the Moon for all launch attempts were negative! (This diagram shows the age/declination phase at arrival). This is a direct consequence of having the launch site in the northern hemisphere and using a direct ascent. It was simply not possible to reach the Moon at declinations above the celestial equator without resorting to the parking orbit technique of later flights.

Trajectory data for Pioneer-1 and the actual and intended flight path. 

The values in the table below contain values from  (2 ) converted to metric units.

Actual injection conditions for Pioneer-1

Flight phase Parameter Value
Launch Time 0842:13 UT, 11 October 1958
  Time 0847:20 UT, 11 October 1958
  Altitude 430.05 km
  Latitude 30.7 N
  Longitude 71.07 W
  Velocity magnitude 10.5230676 km/s
  Velocity azimuth 70.43
  Velocity angle from vertical 64.74
Apogee Altitude 113784 km
Re-entry Time from lifr-off 43 hours 17.5 minutes
  Latitude 21.0 S
  Longitude 88.1 W

The velocity vector for Pioneer-1 was 5 degrees from the intended azimuth. Therefore the intended azimuth is set at 75.43 degrees. The speed at injection for the intended flight path is not so easy to determine exactly from (2 ). There are several values given as you can see from this table:

Various intended injection conditions for Pioneer-1 derived from (2)

Speed given at V = speed at injection h = altitude at injection Total energy (km2/s2)
Page 4 35216 fps (10.73384 km/s) 224 n.m (415.07 km) -1.068813
Page 57 35400 fps (10.78992 km/s) 200 st.m (321.8 km) -1.282107
Page 83 35206 fps (10.73079 km/s) 1410 k.ft (430.05 km) -0.972437
Page 4=v
(Page 76=h)
35216 fps (10.73384 km/s) 1410 k.ft (415.07 km) -0.939725

By using the actual injection parameters the orbital elements and other characteristics of Pioneer-1 can be calculated (see table below) by using classical Keplerian mechanics (3). By using the last line in the table above the orbital elements and other characteristics of the intended trajectory of Pioneer-1 can be calculated in the same way. The reason for ignoring the velocity given on page 83 is that I think it is a misprint. The actual speed should be as given on page 4 - in my opinion. The apogee and period of the calculated orbit for the actual injection conditions match the data in (2 ) reasonably well. The apogee of the orbit resulting from the intended injection conditions also looks reasonable. The negative perigee is caused by the steep flight path angle at injection.

Computed orbital elements

Orbital element etc..



Apogee (km) 113477


Perigee (km) -874


Inclination () 35.79


RAAN () 25.28


Argument of Perigee () 7.90


Angle from node () 60.3


True anomaly () 53.15


Mean anomaly () 1.2


Time from perigee (min) 8.4


Time perigee-to-apogee (hrs) 21.7


Period 43 h 24 m 11 d 6 h 5 m
Declination of apse line () -4.2


Sun aspect angle at injection () 52.3



The map above comes from (2). The map below was generated by my own orbit analysis software SMX using the orbital elements derived from the actual injection condition. Time is shown at the same interval as in the map above. The radio horizon for the tracking station on the island of Hawaii is shown (yellow dot). The two graphs are reasonably similar.

The map below shows the ground track during the first 12 hours for the actual mission and the intended mission. The thicker track marks the part of the flight when the probe is above the horizon at Jodrell Bank (marked yellow). The other sites (Cape Canaveral, Singapore, Millstone Hill) are shown as green dots. One can clearly see the diffence in flight azimuth.

The two ground tracks quickly deviate from each other, but how soon was this evident as seem from the tracking station?The two graphs below show elevation and azimuth of the actual and intended mission as seen from Jodrell Bank. Clearly, by the time the probe rose above the horizon at Jodrell Bank the elevation angle was almost 5 degrees too low and it must have been obvious that the probe would not reach the Moon. 

One can compare the blue graphs with the figure below from (2). The agreement is reasonably good.

I have tried to compute the motion of the probe relative to the Moon in the case of disregarding the gravititaional effects of the Moon in order to try to see what a "patched-conic" analysis might bring. When the probe reached about 65000 km from the Moon about 55 hours after launch its speed relative velocity was 1.27 km/s and it possessed a total energy of 0,73 km2/s2 relative to the Moon. To obtain capture the spped would have to be reduced by 0.88 km/s. In (2) it is stated that the probe's retrorocket had a delta-v capability of 0.85 km/s - about the same! So, the computed trajectory is probably not so far from what was actually intended. One parameter that may be changed to obtain a more plausible trajectory is the injection azimuth. It could possibly be a little higher than the 75.4 degrees used in this analysis. Pioneer-2 flew at an azimuth of 77.0 degrees.  Anyway, the graph below shows the motion of the Moon and the computed intended trajectory and the computed actual trajectory.


  1. Swedish evening paper Aftonbladet, Thurday, 26 November 1959
  2. 1958 NASA/USAF space probes (Able-1), Final report, Vol. 1, Summary, Space Technology Laboratories, 16 February 1959.
  3. R Bate, D Mueller, J White, "Fundamentals of astrodynamics", Dover Publications, New York, 1971.

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