A successful Explorer III launch!

On Sunday, 23 March, I left again for Cape Canaveral to help with the final prepara­tions for the Deal IIb launch. I arrived at Cocoa Beach late that evening and checked into the Coral Sands Motel on the Cocoa Beach strip.

Even then, planning for a future satellite instrument was occupying a significant portion of my attention. On the previous Thursday, during a phone discussion with Van Allen, I indicated that (1) after my trip to the Cape for the launch, I would stop at ABMA for further discussions of the new IGY Heavy Payload (eventually orbited as Explorer 7, as discussed in Chapter 14), (2) I had given the ABMA engineers the power and size requirements for our new instrument, (3) I would be sending him a list of parts to be ordered for its construction, (4) the transmitter power output would

CHAPTER 10 • DEAL II AND EXPLORERS II AND III 281

be about 0.5 watt, (5) we discussed the placement of the GM counter in the payload, and (6) we agreed on a scaling factor of 512 to reduce the counting rate of the GM counter to a value that could be conveyed over the telemetry system.

On Monday, after making my way to the Cape installation, I learned that the JPL engineers had experienced continuing payload problems. Several of the instrument packages interrogated themselves spontaneously—the result of the increased receiver sensitivity built into the flight packages, combined with the complex radio frequency environment in the area. The engineers installed additional filters in the payloads to correct that problem. The data tape recorder in Payload III skipped some of its pulses, and the engineers substituted the recorder from Payload IV. Then a wire from the release solenoid in that recorder broke off, and they replaced the solenoid with the one from the unit they had just removed.

Fortunately, the recorder in Payload II worked perfectly all through the prelaunch testing, and that payload was eventually selected for launching. It continued to operate perfectly on launch day, both for recording and interrogation. In orbit, its operation was flawless throughout the satellite’s entire operating lifetime.

It has always disturbed me that getting the mechanical recording system to operate dependably was such a problem. Today, it would be relatively easy to fabricate a much less troublesome nonmechanical system with solid-state components. But in 1958, we were pushing the state of the art. I believe that the system in Explorer III was as good as I could have made it at the time. I have always realized that a considerable amount of luck was involved in getting the system in Explorer III to operate so well in space.

The launch countdown was a reprise of the Deal IIa launch, except that it progressed with even fewer hitches. The preflight check on the satellite began at 5:12 AM EST on Wednesday, 26 March 1958, with the countdown clock at X – 380 minutes. A low-power system cosmic ray background rate check was begun at 8:09 AM. We made an interrogation check of the onboard recorder at 8:47 AM and a frequency check two minutes later. By that time, the launch countdown had progressed to X – 165 minutes. We made another spot check of the satellite payload at X – 50 minutes. At that time, a hold had been prescheduled to provide time to catch up in case there had been delaying problems. There had not been, so we simply relaxed and waited during that hold.

Van Allen was in the Pentagon again for the launch. While I was listening to the progress of the countdown in the blockhouse, Van was following the same voice comments via a communication circuit between the Cape and Washington. He jotted down the essential content of those comments in his field notebook, which has been

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preserved as part of the collection of Van Allen Papers in the University of Iowa Libraries, Department of Special Collections. They provide an excellent impression of the progress of a typical rocket-launching countdown during that era. The excite­ment of the occasion is evident in the notes, extracted here in slightly abbreviated and paraphrased form. His notes began soon after 11:00 AM, when the count was resumed14:

26 March 1958. 11:05 A. M. EST. Picked up count at X – 50. Surface weather raining, but not to a deleterious extent.

11:30. As scheduled, the count is holding at X – 30.

11:39. [Predicted] values for 24 March are as follows:

Range at Injection: 775 km.

Initial Perigee height: 352 km (219 mi.)

Initial Apogee altitude: 2043 km (1269 mi.)

Time, Liftoff to Cutoff: 152.7 sec.

To Thrust decay: 155.7 sec.

To Separation: 157.7 sec.

To Second Stage: 396-404 sec.

To Third Stage: 404-412 sec.

To Fourth Stage: 412-420 sec.

Time, Liftoff to Injection: 420 sec.

Nominal firing time 12:30.

11:50. The local weather is improving at the Cape.

12:15. The count is X – 17.

All vehicles have left the pad.

12:20. The pad is clear of all personnel.

12:20. Telemetry checks are being made.

X-12 at 12:20 EST.

Holding at X – 10 as of 12:22. The reason for the hold—checking the beat-beat [tracking system] indications.

The count has been resumed at X – 10 as of 12:28 EST.

Cluster spinup has been started.

Range instrumentation has been checked out and no difficulties have been found.

X – 8 at 12:30 EST. The Cluster has reached 350 rpm.

The Cluster is up to programmed speed and the cluster ignition test signal has been checked. X-5 at 12:33 EST.

X – 4 at 12:34 EST.

All instrument panels have been checked out with no trouble.

X-3.

X – 2.

The range is clear at X – 90 seconds.

X – 1 [minute].

– 50 sec.

– 40 sec.

All preparations complete.

– 20 sec.

– 10

Firing command.

At the Cape, I noted that the work to improve the reliability of the satellite command system and onboard tape recorder had paid off, as there were no problems while the upper-stage tub was spinning. I monitored the signals from the Iowa instrument

CHAPTER 10 • DEAL II AND EXPLORERS II AND III package throughout the countdown and gave my OK on instrument performance after cluster spin-up and finally once again just a few minutes before ignition.

Liftoff occurred at about 12:38 PM EST on Wednesday, 26 March 1958, only eight minutes after the originally scheduled time. The rocket disappeared quickly into low cloud cover, and final injection into orbit occurred at about 12:46. As the payload disappeared from radio range, the Doppler shift looked good, signifying a proper velocity in its path away from the Cape.

I was impressed once again by the sense of overwhelming power as the rocket lifted off and accelerated away from us. I was talking on a phone at the time, giving the liftoff details to the NRL receiving station in Hangar S, where they were also tracking it. As soon as ignition occurred, I could no longer hear my own voice at all, even though I was shouting into the phone.

Van Allen’s field notes continue to provide a vivid account of the ascent and injection:

Ignition normal—main stage.

Liftoff.

Exhaust plume looks good.

Tilt program has started.

Beat-beat indications are good.

Acceleration appears normal.

12:39. Following trajectory very closely.

Program and lateral acceleration are good.

Programming of cluster speed proceeding as planned.

Tilting program completed.

First stage cutoff OK.

First stage] launch was normal. Cluster and instrument compartments are now coasting to apex.

During this coasting period, the variable jet nozzles are aiming the upper stages to the pre-calculated angle for injection.

The on board timer is to ignite the second stage at 396 seconds after liftoff.

12:45. All four stages ignited according to all indications.

12:58. Pickering reported Antigua interrogated successfully.

At the Cape, I, too, learned that the down-range Antigua Minitrack station had made a successful interrogation of the onboard tape recorder soon after the final rocket firing. Only a single command transmission was required, a strong signal containing a two second recorder readout was received, and the tape recorder was reset for its first orbit.

A simplified Minitrack station at Johannesburg, South Africa, acquired the low – power signal as the satellite passed overhead, but it was too early to reveal whether or not the satellite had achieved a durable orbit. As in the case of Explorer I, there was a long delay before we could confirm that the payload was in orbit.

The observers at the Pentagon learned that a receiving station at the Naval Or­dinance Test Station near Inyokern, California, received the new satellite’s signal beginning at about 14:34 EST (19:34 UT). I did not have access to that information at the Cape, but I soon learned there that the low-power transmitter signal was received

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in quick succession at the Microlock stations at JPL (19:35:05 UT), Earthquake Valley (19:37:33 UT), and Temple City (19:39:55 UT). The Vanguard project’s San Diego Minitrack station also received the signal at about the same time that Earthquake Valley received it.

Such conclusive receipt of the low-power transmitter signal at the completion of the first orbit caused great jubilation. Determining whether the full cosmic ray instrument package was operating properly took more time, however.

Only the Vanguard Minitrack stations had the equipment for commanding the readout of the onboard recorder. The only such station on the West Coast was the San Diego station. They attempted repeatedly near the end of that first orbit to interrogate the recorder but were unable to detect any response. Hearing that, my heart sank, as recovery of the onboard stored data was essential if we were to achieve the full objectives of our experiment.

I remained at the listening post at Cape Canaveral to sweat out the next orbit. For the pass at the end of the second orbit, the Minitrack station at Quito, Ecuador, had the primary data recovery and tracking responsibility. They received the low-power signal and made a series of 10 command transmissions but were unable to detect any response of the high-power system. Our hopes were buoyed a bit, however, by a report that the Lima, Peru, station, marginally within range, might have heard a faint response from the data recorder.

I went from the Cape to Huntsville to discuss the new IGY Heavy Payload. It was not until early afternoon on the 27th, in Huntsville, that I was finally able to get in touch with Jack Mengel in Washington and learned with tremendous relief that some of the subsequent attempts to read the in-flight recorder had produced better results. By that time, receipt of onboard recorder data dumps had been reported from 5 of 12 satellite passes. I was ecstatic!

During the telephone conversation with Van Allen on launch day, in addition to the discussion about the new satellite planning, he asked that I arrange to bring one of the Explorer I spare payloads back to Iowa City for further calibration checks.

Van returned to Iowa City from Washington that evening. During a stop in Chicago, he called Jack Mengel and received the same information that I had received at the Cape, that is, that the Quito interrogation had apparently been received at Lima. On the next day, he received the same news that I was receiving at Huntsville, that is, that 5 of 12 attempts had been successful.

The further history of Explorer III operation is picked up in the next chapter.

Explorer III’s final velocity was higher than the planned value, so that the maximum orbital height (apogee) was quite high. We found, however, that the final stage was pitched up by from four and a half to six degrees from the horizontal when it fired, resulting in a somewhat lower minimum height (perigee) than planned. The initial

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calculations at the NRL Computer Center on Washington’s Pennsylvania Avenue indicated that the perigee height might be as low as 60 miles, which would result in only a two week orbital lifetime before the satellite’s velocity would be slowed by atmospheric drag and it would plunge earthward. By the next day, however, a greater accumulation of tracking data and hard through-the-night work by Joe Siry’s orbital computation team yielded more accurate orbit parameters, including a perigee height of 125 miles and an apogee height of 1735 miles. Based on that new information, the orbital lifetime was projected to be from four to six months, plenty of time for us to conduct our experiment.

Parenthetically, with the higher-than-planned apogee, the satellite turned out to be even more helpful in delineating the anomalous high-intensity radiation than it might have been at the nominal heights.

Explorer III with its attached rocket stage, like Explorer I, spanned 80 inches in total length and six inches in diameter. The total weight placed in orbit was 31.00 pounds, of which 10.83 pounds was the satellite instrument, 7.50 pounds was the shell, and 12.67 pounds was the exhausted final rocket stage.

The initial orbit ranged from 116 miles at perigee to 1739 miles at apogee, with an inclination relative to the Earth’s equator of 33.5 degrees. The initial orbital period was 114.7 minutes. The satellite reentered the Earth’s atmosphere on 28 July 1958.

I was anxious to get to Iowa City following the launch, but, as mentioned above, I had to stop at Huntsville to coordinate our efforts on the new IGY Heavy Payload. Arriving there at midday on Thursday, 27 March, I joined a meeting already in progress. Chaired by Josef Boehm, that meeting dealt with many details of the payload’s mechanical structure and electronic systems. The next day, I met with H. Burke to further discuss electronic circuits, and then again with Boehm on overall project planning. By that time, my notes were frequently referring to the IGY Heavy Payload as the Juno

II project. Further details of that meeting and the follow-up work are described in Chapter 14.15

It was finally possible to leave Huntsville for Iowa City at noon on Friday, but I was frustrated en route by tardy plane departures and missed connections that forced me to remain overnight in Chicago. In a rather foul mood, as I sat waiting at the Chicago airport, I wrote a note that reflected considerable frustration at the situation then facing me, in spite of the exhilaration of the successful launch:

Had a successful visit at Huntsville. But it looks like Juno II will be another crash program. The first two packages (SUI’s part) are to be done by May 1. Looks like I’ll have to rush back to Iowa, or at least to the Iowa payroll. What a life!! I’m getting a little weary of this rat race—after over two years of it. It will be nice to settle down to school for a while, if that ever happens.16

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Since the pressure for me to move ahead quickly with the Juno II circuit design was so intense, my stop in Iowa City was fleeting. Arriving there at mid-morning on Saturday, 29 March, I had several conversations with Van Allen and the others. Although the preliminary indications from the Explorer I data were hugely intriguing, my personal preoccupation during that visit was to brief our team on the results of the Juno II planning meeting.

During spare moments on that trip, I continued writing a paper describing the Explorer I instrument.17 I left Iowa City for my return to Pasadena at about noon on Monday, 31 March.

Endnotes

1 George H. Ludwig, Laboratory Notebook No. 57-6, covering 10 September 1957 to 30 June 1958, p. 33. Undated entry. Also see George H. Ludwig, JPL internal memorandum to Milton Brockman, “To prepare package for spin test,” 25 November 1957.

2 George H. Ludwig, Laboratory Notebook No. 57-6, covering 10 September 1957 to 30 June 1958, p. 51. Entry dated 9 December 1957.

3 Walter K. Victor, Inter-office memorandum to JPL Cognizant Engineers, “Deal II Standard Operating Procedures and Scheduling,” 13 December 1957.

4 George H. Ludwig, letter to James A. Van Allen, 22 January 1958.

5 Ibid.

6 Ludwig, Laboratory Notebook No. 57-6, p. 51. Entry dated 9 December 1957. Also George H. Ludwig, Journal covering 19 September 1956 to 23 August 1960. Entry dated 18 February 1958.

7 Ludwig, Journal covering 19 September 1956 to 23 August 1960. Entry dated 20 February 1958.

8 George H. Ludwig, JPL Travel Report, 20 March 1958.

9 Ludwig, Laboratory Notebook No. 57-6, pp. 96-99. Entries dated 3 and 4 March 1958.

10 George H. Ludwig, Journal covering 19 September 1956 to 23 August 1960. Entry dated 5 March 1958.

11 Richard Witkin, “2D U. S. EXPLORER FIRED, VANISHES; ORBIT IS IN DOUBT,” The New York Times, 6 March 1958.

12 The results of these tests were described in H. R. Buchanan, JPL inter-office memorandum to Walter K. Victor, “Deal II ‘Turn-On’ Receiver Sensitivity Tests,” 14 March 1958.

13 Robert L. Choate, “Calibration Records for the IGY Earth Satellite 1958 Gamma,” JPL Publication No. 126, 27 June 1958.

14 James A. Van Allen, field note pad entry dated 26 March 1958, located in “Papers of James A. Van Allen,” University of Iowa Library Archives, Iowa City, Box 384, folder 2.

15 The meetings during that visit are recorded in George H. Ludwig, Laboratory Notebook No. 58-8, covering 2 to 18 April 1958 and 30 June 1958 to 2 January 1959, pp. 136-137. Entry dated 2 April 1958.

16 George H. Ludwig, Journal covering 19 September 1956 to 23 August 1960. Entry dated 28 March 1958.

17 George H. Ludwig, “Cosmic-Ray Instrumentation in the First U. S. Earth Satellite,” Rev. Sci. Instrum., vol. 30 (AIP, April 1959) pp. 223-229. Reprinted in IGY Satellite Report, no. 13 (Wash., DC: Natl. Acad. Sci., January 1961).