From the Wikipedia article Pioneer P-30:

At an altitude of about 370 km (230 mi), the first stage separated from the second stage. When the second stage was ignited, telemetry showed abnormal burning, and the stage failed due to a malfunction in the oxidizer system. The vehicle was unable to achieve Earth orbit, re-entered, and was believed to have come down somewhere in the Indian Ocean. Signals were returned by the payload for 1,020 seconds after launch. The mission was designed to reach the Moon approximately 62 hours after launch. Although the mission was a failure, ground controllers fired Able VA's onboard liquid propellant hydrazine rocket engine — the first time that an onboard motor was fired on a space vehicle.

The 2010 post Topic: Able IV: World's first space engine (1959) at Collect Space dot com give a sighting of an un-flown engine in 1970.

Since some were launched, and one even ignited in space successfully, there must be, or have been at least one on the bottom of the ocean (unless there were heroic recovery efforts).

Question: Where are they now? Are there any currently on public display? Were any of these historical items ever recovered?

"Bonus:" Why is it notable that this started in space, and why is it different than second stages (including the one in this mission) starting in space? What is the "firstness" here?

In 1960, STL built two more hydrazine monopropellant space engines of the same design and designated Able V-A and Able V-B. These engines were launched September 25, 1960 (Pioneer P-30) and December 15, 1960 (Pioneer P-31). Unfortunately, both launches failed shortly after lift off. However, on the 17 minute Pioneer P-30 mission, the Able V-A engine got to see action. Despite a subpar second stage burn which prevented the Pioneer from reaching escape velocity, ground controllers were still able to fire the Able V-A engine. Therefore, STL’s Able IV/V space engine design “was the first to successfully ignite and operate in space.”

Descendants of the Able IV engine are still in use today. Thanks in part to the pioneering efforts of STL, hydrazine engines can be found maneuvering the International Space Station, the Space Shuttle, communication satellites, and more.

TRW presented the remaining Able IV space engine to a retiring VP in 1970.

There are are archived goodies for reference material - see here also.

below: Abel, the world's first space engine.

enter image description here

  • 1
    $\begingroup$ "and why is it different than second stages (including the one in this mission) starting in space? " Probably zero-gee starting capability. $\endgroup$ Apr 7 '17 at 19:23
  • 1
    $\begingroup$ @OrganicMarble Wait, why wouldn't a second stage in a ground-intercepting elliptical orbit (otherwise known as suborbital) be just as zero-gee as a deep space start? I still don't see the difference. Is it the small amount of drag? $\endgroup$
    – uhoh
    Apr 8 '17 at 4:24
  • $\begingroup$ Ullage maybe?.. $\endgroup$
    – SF.
    Mar 28 '18 at 17:41
  • $\begingroup$ "the first time that an onboard motor was fired on a space vehicle"... doesn't that record belong to the Luna-1 mission on 2 jan 1959? Pioneer p30 was in sep 1960. $\endgroup$ Oct 20 '21 at 14:50
  • $\begingroup$ @PcMan that's a block quote from the linked Wikipedia article. It has a talk page where issues like that can be discussed, or you can post a new "Is Wikipedia wrong?" question. $\endgroup$
    – uhoh
    Oct 20 '21 at 15:50

The only surviving model of the Able IV spacecraft is privately owned and not in public display. As mentioned in an article of the Explorer magazine published by the American Astronautical Society (AAS) (Issue 10, March 2010, page 7):

Robert Enichen of Yardley, Pa., is the proud owner and humble caretaker of a piece of space history — one of the first series of liquid-fueled rockets to fire in space. Originally, TRW presented this 1959 vintage Able IV space engine to retiring TRW Vice President Ed Robinson, an avid engine collector. Enichen acquired the space engine after Robinson decided to wind down his collection. Enichen graciously provided pictures of his engine aswell as an article on its history.

As you mentioned in your question Able V-A and V-B were on board launches that failed, so most probably they were destroyed on the launch pad (in the case of V-B) or crashed in the ocean (in the case of V-A) and never found.

You can see a picture of the Able IV spacecraft bellow:

enter image description here

This and other photos can be found at Robert Enichen's website.

As for the question of the difference between Able's engine and a common second stage engine, the answer can be found in his website:

The monopropellant hydrazine (N2H4) fueled Able IV engine was capable of multiple restarts in space allowing midcourse velocity correction and retro propulsion to adjust the spacecraft’s trajectory en route to the planned lunar orbit. Previously, rocket engines burned continuously until their fuel was exhausted.

  • $\begingroup$ Excellent detective work and sourcing. Thank you! $\endgroup$
    – uhoh
    Sep 19 '18 at 11:34
  • $\begingroup$ I had almost finished writing a second comment when you deleted your answer. I wonder if you might copy/paste it as an answer to this question instead? What would a “Kármán plane” look like, a bird, or a plane? If you look at your profile page you can find it by clicking recently deleted questions at he bottom of your question list. It was a great answer, and I think it fits much better here. $\endgroup$
    – uhoh
    Oct 18 '18 at 9:52
  • $\begingroup$ Hey I liked your answer and I hope it returns! It looks great with the link, It's morning here and I've just deleted my comment. $\endgroup$
    – uhoh
    Feb 11 '19 at 0:47

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