Peace activists are planning to protest on Wednesday against a launch of a United States military satellite by Rocket Lab, but by then the first satellite they are concerned about may already be in space.

Police have indicated they had been taking an interest in assessing sentiment towards the launch, visiting a concerned community member to discuss social media posts.

Rocket Lab will conduct its 18th orbital mission from the Māhia Peninsular some time from late Tuesday morning, depending on the weather.

One of the satellites on board, dubbed Gunsmoke J, was commissioned by the US Army's Space and Missile Defence Command (SMDC).

US defence documents indicate the satellite is the first of a series of satellites that will carry advanced electronics that could provide "tactically actionable targeting data to warfighters" – in others words could help direct fire in a conflict.

A few weeks ago an open letter was sent to Prime Minister Jacinda Ardern by the Peace Foundation International Affairs and Disarmament Committee, expressing concerns the launch could violate the nuclear-free law.

The letter said the Gunsmoke-J satellite could be used to target nuclear weapons as well as conventional weapons systems.

As part of the Space For Peace campaign there is a peace march hikoi in Māhia planned for Wednesday at 11am to 2.30pm in Opoutama.

Protesters plan to meet at the village pou and march along Rongomaiwahine drive, along the beach and back to the pou.

The protest was being organised by members of the community and supported by Rocket Lab Monitor group.

Rocket Lab spokeswoman Morgan Bailey said she was not aware of any protests being planned for launch day.

“But it has been a mission that has caused a lot of interest, so we will have to wait and see," she said.

A Wairoa woman was contacted by police after setting up the website Rocket Lab Monitor, which collects information and education about Rocket Lab and the space sector in New Zealand.

The website and went live on February 15, and she received a call from police on March 2.

“Everything we wanted to know seemed difficult to find and shrouded in mystery. All of us had a mutual feeling of unease”, the woman told Stuff.

“Our concerns were furthered by other whanau who were shareholders of the Tawapata block who couldn’t answer any questions and were frustrated as they had shared concern.”

The woman said she was “surprised” police wanted to talk to her.

“My actions related to Rocket Lab were constructive and pretty fresh so at that point I knew there was a high level of monitoring.”

A police spokesperson said police's role was to ensure that all members of the community were “safe and feel safe.”

“Part of this includes engaging with community leaders, in order to understand their perspectives and what is happening across the rohe, to ensure we can provide the best possible service to our people.

“We did visit an individual in relation to some Facebook posts; they were open and willing to speak with police.”

Rocket Lab completed rehearsals for the launch on Friday, and as of Monday afternoon was still hoping for a launch on Tuesday.

Notices of the intended launch date were published in local newspapers "a couple of weeks ago" but Rocket Lab did not tend to publicise these on social media before rehearsals had been completed, Morgan said.