Pioneer Venus and the Intel 4004

Most recent revision date of this page, July 19 2019. Copyright 2019 Herb Johnson. This is a preliminary "stub".


Thanks to a reference by Greg Levin in a July 2019 email-list post on a vintage microprocessor, I learned that a Pioneer Venus spacecraft, lanunched in Aug. 8, 1978, contained an Intel 4004 processor. Further research led to published accounts on the engineering of instruments on Pioneer Venus and ultimately to a specific reference to the "Large Neutral Mass Spectrometer", on the "Large Probe" which plunged into the Venusian atmosphere. That instrument contained the Intel 4004. Details follow below. - Herb Johnson

When were microprocessors used in space?

The earliest microprocessors - single or dual chips which performed stored-program computing operations - were first created and produced in the mid-1970's. This was decades after the first satellites of the late 1950's. So early satellites were built using controllers or sequencers built from various "descrete logic" devices, or analog electronics and mechanics. Later satellites incorporated various microprocessors of the times - as the chips were "rated" for operation at low power, for stability, and for radiation-tolerence.

I was informed about the early use of the RCA "COSMAC 1802" in space, by reports and email discussions by Steve Gemeny. Steve worked on some early spacecraft projects at JHU/APL; and he's an enthusiast still for the COSMAC 1802. I followed his discussions and publications, then corresponded with him. Also I did literature searches on the subject of mid-1970's spacecraft and their controllers and instruments.

In Dec 2009 I worked to dispell a myth that spacecraft like the Voyager (now extra-planetary) craft, or the Mars Viking lander, contained the 1802 microprocessor. They did not, as established by review of NASA documents and publications; they were operated by minicomputer-like reprogrammable controllers. They were designed before the mid-1970's development of the 1802.But the 1802's CMOS construction, low-power and radiation-resistant, was suited for space; it was used in early amateur-radio satellites and later in NASA's Galileo and other spacecraft.

And so, until July 2019, I believed the "first microprocessor in space" was an Applied Physics Lab designed Earth-orbited spacecraft named "MAGSAT", launched Oct. 30, 1979. It was followed by the first AMSAT Phase III satellite to reach orbit, in 1981. Read this account of those early use of the COSMAC 1802 in space. For use of COSMACs in amateur radio satellites, here's an account I produced. All dates and technical details, are referenced to primary sources and documents.

A hint of an earlier processor in space

It took some time, for various Web sites to correct themselves about "Voyager's COSMAC microprocessor". But individuals continued to recall the prior incorrect information. One such person, posted something to that effect, in the cosmacelf discussion group on in July 2019 under the thread "Voyager 1". The person was called to task, and informed about my Web page.

But then, Gregg Levine posted in the cosmacelf thread on July 13: "I happen to know that micros such as the CDP1802 didn't start making adifference in our satellites until about the time of the Pioneer Venus mission. There they used a version of the Intel 4004 (or 4040) one." I posted in reply that I was skeptical but I'd check it out.

The Pioneer Venus mission

As any number of NASA-supported Web pages describe the Pioneer Venus mission and spacecraft. It consisted of two spacecraft: the Orbiter and the Multiprobe, launched seperately. The Orbiter was launched on May 20, 1978. It reached orbit around Venus on Dec. 4, 1978. The Multiprobe was launched on Aug. 8, 1978 and reached Venus on Dec. 9, 1978. The Multiprobe consisted of four "small probes" and one "large probe" which plunged into the Venusian atmosphere to sample and analyse it. The small probes were released from the "Bus" of the Multiprobe on Nov 15th, the large on the 19th of 1978. They entered the Venus atmosphere also on Dec 9th, and within an hour or so crashed on the Venus surface while delivering data to Earth. The Orbiter achieved Venus orbit and provided mapping, radar, imaging and planetary data well past its expected mission. Most Orbiter instruments still operated, when that spacecraft entered the atmosphere on Oct. 8, 1992.

The story of Pioneer Venus, the last of NASA's Pioneer planetary spacecraft, is an exciting read, from mission conception, through planning and funding, design of craft and instruments; then launch, arrival at Venus, and the success of probes and orbiter. Much of the publications about Pioneer Venus, are about the data collected from the dozens of instruments. There's numerous accounts of each of the instruments, written by the Principle Investigators who built them, operated them, and processed and reported data from them. There's accounts of the general features of the spacecraft. There's detailed accounts of the process of funding and launch, the tick-tock of events thru the missions. I'll provide a bibliography at the end of this Web page.

Engineering hardware on Pioneer Venus

But it's hard to find specific, "engineering" information about the spacecraft's controlling hardware, or about the hardware details of the instruments. However, a few of the general accounts of the mission, and a few about instrumentation, included information about "the microprocessor" and where and what it was.

No reference suggested the spacecraft were controlled by microprocessors. My impression is that Pioneer Venus used much the same controller technology as the previous ten Pioneers. A few references said, "the Neutral Mass Spectrometer contained a microprocessor" - but did not name brand or model. In due course, I found one NASA publication which was specific and insisted quote "It also used the first microprocessor to fly in space: an Intel 4004." I'll quote text and images from it for my references.

A microprocessor on Venus


Pioneering Venus : a planet unveiled

"Pioneering Venus : a planet unveiled"
by Fimmel, Richard O; Colin, Lawrence; Burgess, Eric
prepared at NASA Ames Research Center
ISBN 0-9645537-0-8 hard, ISBN 0-9645537-1-6 pbak.
QB621.F55 1995, 523.4.2--dc20 

As of July 2019, a copy of this book was available as scanned, on the Internet archive at, under the "Pioneering Venus" name and the first-named author. The book was published in 1995 by the US Govt. Printing Office, and thus is freely available for reference and copy: "our tax dollars at work". There's similar publications which describe the Pioneer Venus mission in chronologic and technical detail. But this was the first I found which stated "the Intel 4004". The next section of this Web page, quotes its description of the in the Large Probe, and its reference to the controlling microprocessor. I've shortened the text with comments in []'s to explain the edits, or to note the pages referenced.

Large Probe


The Large and Small Probes were similar in shape. The main component of each probe was a spherical pressure vessel. Machined from titanium, the vessels were sealed against the vacuum of space and the high pressure of Venus's atmosphere. Within this pressure vessel were scientific instruments and various subsystems for the probe's operation. The Large Probe weight about 315 kg (695 lb) and was about 1.5M (5 ft) in diameter (fig 3-17). It consisted of a forward aeroshell heat shield, a pressure vessel and an aft cover... The pressure vessel (fig 3-18) was 73.3cm (28.8 in) in diameter. Four scientific instruments use nine observation windows thorugh four of the pressure vessel penetrations. Eight windows were sapphire and one was diamond. [page 69-72]

[The Large Probe, Small Probe, and the Orbiter were described as containing "Command/Data Units" but no engineering description was given of them, other than "sequencers". ]

The Large [Probe] Neutral Mass Spectrometer

Challenges of Instrument Development: Probes [pages 31 following]

The neutral mass spectrometer was a principal development challenge. One main difficulty was to develop an inlet system for the instru- ment. [Discussion of the problem followed.]

The mass spectrometer caused even more difficulties. A single inlet would be fine in the dense lower atmosphere. But in the upper rarefied atmosphere, this instrument needed an additional inlet to provide sufficient gas input. [details of inlet design followed].

In addition to its novel inlet design, this instrument had several other firsts. It was the first mass spectrometer of its size to survive the forces from an entry deceleration of 400 g. It also used the first microprocessor to fly in space: an Intel 4004. The microprocessor allowed the spacecraft to take a full spectrum of data once every minute over the whole mass range of 200 amu. The microprocessor selected the true data point from several data points and adjusted for calibration changes. A high confidence factor was associated with the single data point transmitted. Without the microprocessor, it would have been possible to transmit a spectrum only once for every 10-km change in altitude. With the micropro- cessor, sampling occurred at every 1-km change in altitude. [page 32]

Neutral Mass Spectrometer [pages 105-8]


The neutral mass spectrometer (Figure 4-13 [page 107]) measured the composition of the lower 62 km (38 miles) of Venus' atmosphere. This region was mostly below the cloud layers. Information on the relative abundance of gases in this region was important. With it, scientists could better understand the planet's evolution, structure, and heat balance.

The spectrometer, which weighed 10.9 kg (24 lb) and required 14 W of electrical power, consisted of two units. Both units were on a single baseplate on the probe's lower shelf. A mass analyzer, ion source, pumping system, isotope ratio measuring cell, and valves were in one unit. Electronics were in the other. The principal investigator was J. H. Hoffman, University of Texas, Dallas.

The instrument had wide dynamic and mass ranges to survey atmospheric gases and determine cloud composition. Its design made sure that the sampling process did not alter chemically active species. To prevent such alteration, it collected samples through a chemically passive inlet leak.


The inlet consisted of a pair of microleaks, each formed by compressing the tip of a tantalum tube into a slit. The tubes projected through the probe wall to beyond the boundary layer. When the atmospheric pressure reached 1.5 bars, the tube with the larger conductance closed off. This prevented too large a sample deeper within the atmosphere when pressure increased rapidly. Atmospheric gases and vapors were pumped into an ion source through a variable conductance valve.

During descent, the valve gradually opened to keep a constant pressure at the ion source. A magnetic sector field mass spectrometer analyzed the gas sample. Its range was 1 to 208 atomic mass units. The spectrometer detected minor constituents in 1-ppm concentration over the entire descent. To identify unknown substances and separate parent peaks from fragmentary ions, ionizing electron energy was stepped through three levels.

Each mass spectrum took 64 seconds to sample. A microprocessor controlled the mass scan mode, sequencing of ion source energy, and data accumulation and formatting. The instrument converted accumulated counts for each spectral peak into 10-bit, base-2, floatingpoint numbers. With a rate of only 40 bits/sec, the spacecraft successfully transmitted to Earth data from about 50 spectra obtained during the descent.

The instrument used an isotope ratio measuring cell to collect a sample shortly after the parachute's deployment. In this cell, the sample was purged of carbon dioxide and other active gases. After purging, an enriched sample of inert gases was left. Then the device pumped out the ion-source cavity and analyzed the sample to determine the isotope ratios of such inert gases as xenon, argon, and neon. All these gases are important for understanding how Venus' atmosphere evolved. [page 108]

References about Pioneer Venus

"Pioneer Venus", NASA SP-461, by Fimmel, Colin, and Burgess, 1983, appears to be similar to the "Pioneering Venus" text quoted above, and has much the same text. Page 23 of the document also says "this instrument also used the first microprocessor to be flown in space: an Intel 4004".

NASA or US Government agencies, produced a number of Web sites over the decades about NASA spacecraft; and published a number of books and documents. It's bewildering to wade through them, to get specific detailed information. Some sites are data repositories; in this case for the body of data collected by the multiple probes and instruments of this mission, and by decades of data from the Orbiter.

Hoffman on the LNMS

Chapter 31 Space Applications of Mass Spectrometry - NTRS - NASA by JH Hoffman dated 2010? 130 pages

31.12 Pioneer Venus Mission
Large Probe Neutral Mass Spectrometer
Arkin, Griffin, Hoffman, Limero

Scanning of the mass spectrum occurred by stepping the ion acceleration high voltage to successive peak tops under the control of a microprocessor, an Intel 4-bit processor. A preset table of mass numbers including mass defects in the microprocessor defined the voltages for the selected mass numbers. The complete spectrum, consisting of 236 mass peak positions, was scanned at the rate of 4 samples per second in 59 s. A noble gas enrichment cell, the IRMC, was included in the instrument package to collect an atmospheric sample just after initiation of the instrument operation, purge the sample of CO2 and later (just before parachute jettison) introduce the sample into the mass spectrometer for measurement of the isotopic ratios of the enriched inert gases remaining in the cell. [page 107-8]

Other publications on the LNMS and Pioneer Venus

Pioneer Venus large probe neutral mass spectrometer

Several publications are in the linked document. They were uploaded to the site "by R. Richard Hodges on 21 August 2014." They include:

J H Hoffman, R Richard Hodges, K D Duerksen
Journal of Vacuum Science and Technology April 1979
Source: IEEE Xplore

"Final Report, Pioneer Venus Large Probe Neutral Mass Spectrometer"
sub. to NASA by The Univ of Texas at Dallas
grant NAGW-64 E0506-01
Dr John Hoffman, Principal Investitator, May 24 1982
NASA-CR-188963 Pioneer Venus Large Probe N82-24284

J. Vac. Sci. Technol. 18(2) Mar/Apr 1979 pages 882 following
Pioneer Venus large probe neutral mass spectrometer
J. H. Hoffman, R. R. Hodges, and K. D. Duerksen
Center for Space Sciences The University of Texas at Dallas.

After the Large Probe encounters the top of the atmosphere its protective heat shield is ejected and a parashute deployed. Pyrotechnic devices are activated, which break a hermetic cover over the inlet leaks. The inlet leaks are passivated and the tantalum tubes t/s in. in diameter which have been forged into a flat plate configured leak with a leak rate on the order of 1 x 10-7 cma/s. Ambient gases passing through these hemispheres tally passive inlet leaks enter the ion source in a partially cullimated molecular beam. Ionization occurs by electron bombardment and mass analysis by a sector field magnetic nalyzer. Ions following one of the two allowed trajectories through the magnet enter counting system.

The counting rate vs time, relative to a reference time (this determines mass number) is telemetered back to earth as a compressed data word at a rate of 40 bits/s. At this data rate the entire mass spectrum is scanned in only 64 s by a highly efficient peak stepping routine control!ed by a microprocessor. Ionizing eleetron energy is stepped through three levels to provide ?? data on the energy, dependent cracking patterns of gas samples to aid in the identification of unknown substances and the separation of parent peaks and fragmentary, icus. At high altitude the leaks are open, but at about 48 km the sec- ondary leak is eliminated bv closing valve 1, reducing the inflow of atmospheric gas as pressure increases. [page 883]


Pioneer Venus Sounder Probe Neutral Gas Mass Spectrometer

"The purpose of this paper is to describe some of the unique features of the mass spectrometer instrumentation that was used for the Pioneer Venus mission. After a general discussion of the instrument, packaging and mounting in the probe, the atmosphere sampling system and pumping system will be described, followed by the mass analyzer and its operating characteristics and finally the microprocessor that controls operation of the entire instrument, and is thought to be the first such item to have been flown on a deep space probe. [page 81]"

Herb Johnson
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