There are a good choice of hotels nearby ESA ESTEC . The list below gives several examples of places to stay in towns near the conference venue including Noordwijk, Leiden and Sassenheim.

Noordwijk:
Alexander Hotel  – https://www.alexanderhotel.nl/en/
Fletcher Badhotel  – https://fletcher-badhotel-noordwijk.hotelmix.co.uk/
Golden Tulip Noordwijk Beach – https://noordwijk-beach.goldentulip.com/nl-nl/
Grand Hotel Huis Ter Duin – https://huisterduin.com/?lang=en
Hotel Golfzicht  – https://www.golfzicht.nl/?lang=en
Hotel Royal  – https://hotel-royal-noordwijk.hotelmix.co.uk/
NH Noordwijk Conference Centre Leeuwenhorst  – https://www.nh-hotels.com/
Prominent Inn – https://www.prominentinn.nl/
Van Der Valk Palace Noordwijk (previously Radisson Blu Palace Hotel) – https://www.valkverrast.nl/en/hotels/palace-hotel-noordwijk

Leiden:
Golden Tulip Leiden Centre – https://leiden-centre.goldentulip.com/nl-nl/
Hilton Garden Inn Leiden  – https://www.hilton.com/en/hotels/amslngi-hilton-garden-inn-leiden
Ibis Leiden Centre – https://all.accor.com/hotel/8087/index.en.shtml
Tulip Inn Leiden Centre  – https://tulip-inn-leiden-centre.goldentulip.com/en-us/

Sassenheim
Van der Valk Sassenheim – https://www.hotelsassenheim.nl/en