WASHINGTON — As NASA evaluates proposals for commercially developed small lunar landers, the agency is now seeking payloads that could fly on those spacecraft despite concerns from some scientists that they don’t know if their experiments are compatible with those landers.

NASA released Oct. 18 a formal solicitation for “Lunar Surface Instrument and Technology Payloads” that seeks experiments for flight on lander missions procured by the agency’s Commercial Lunar Payload Services (CLPS) program. NASA plans to select 8 to 12 experiments next year for launch no earlier than 2020, with an overall budget of between $24 and 36 million in the first year of the program.

In a statement, NASA said it’s looking for payloads “that advance capabilities for science, exploration, or commercial development of the moon.” That includes, according to the solicitation, work by any of the agency’s four science divisions, so-called “Strategic Knowledge Gaps” for human exploration and technologies needed for future lunar exploration.

“We are looking for ways to not only conduct lunar science but to also use the moon as a science platform to look back at the Earth, observe the sun, or view the vast universe,” said Steve Clarke, deputy associate administrator for exploration in NASA’s Science Mission Directorate, in the statement. “In terms of technology, we are interested in those instruments or systems that will help future missions — both human and robotic — explore the moon and feed forward to future Mars missions.”

However, NASA’s statement listed what it expects some of those first payloads to be: “On early missions, science instruments will likely gather data related to heat flow within the Moon’s interior, solar wind and atmosphere as well as dust detection.”

For this procurement, NASA is looking for experiments that are either already assembled or could be made ready for flight quickly. “We are interested in flight spares, engineering models, modified off-the-shelf payloads, student hardware or any other hardware that can credibly meet the aggressive timeline” included in the proposal, it stated. That timeline calls for delivery of payloads for flight between March 2020 and December 2021.

NASA will procure flights on those payloads through its CLPS program, which plans to make use of commercial lunar landers under development. NASA issued a request for proposals for CLPS in September, with proposals due to the agency Oct. 9.

Clarke, speaking at the International Symposium for Personal and Commercial Spaceflight in Las Cruces, New Mexico, Oct. 10, said the agency expected to make awards in the CLPS program in December. “I’m optimistic we had a healthy response to that call,” he said. “I think I know some of the players who probably proposed, but I’m hoping I’m surprised by others that I didn’t know would propose.”

One challenge for payload developers, though, is a lack of details about the payloads. The payload solicitation offers only basic “engineering accommodation capabilities” for the CLPS landers, including a payload mass of no more than 15 kilograms and a continuous power level of 8 watts.

“Specific payload accommodations may vary by lander provider, and because these lander services are still being developed, the payload accommodations are subject to change,” the solicitation noted. “These capabilities will most assuredly evolve over time, but are expected to approximately represent the initial operating capabilities of the expected lunar landers.”

Clarke, speaking at a Sept. 11 meeting of the Committee on Astrobiology and Planetary Science of the National Academies’ Space Studies Board, said NASA would develop a “prioritization” of the payloads selected through this solicitation to match them up with various CLPS missions, based on those landers’ capabilities, schedules and landing sites.

Some committee members were worried, though, about a potential mismatch between landers and experiments. “It seems to me that the [request for proposals] that is going out to the lander vendors has no concept of what the instrumentation needs are,” said Mark Saunders, a member of the committee, “and the [NASA research announcement] is going out with no concept of what the capabilities of the landers are, thus you could end up with no match.”

“I do think that the work has been done to ensure that there would be matches between the lunar payload call and the lander services call,” Clarke responded, but added he didn’t know the specifics, as much of the planning work had been done before he took his current position earlier this year.